A 401(k) plan is a type of employer-sponsored defined-contribution retirement plan. Its name comes from section 401(k) of the Internal Revenue Code  which defines it. It is also generally governed by Title I of the Employee Retirement Income Security Act of 1974 (ERISA). According to the latest (2008) Survey of Income and Program Participation (SIPP), 60 million individuals (33.0% of the U.S workforce) participated in 401(k) plans. In 2008, individuals made average annual contributions of $4,513 to the plans. The nation's 511,582 401(k) plans held $2.23 trillion dollars at year end 2008. 
- You get an immediate tax break, because contributions come out of your paycheck before taxes are withheld.
- Many employers will match your contributions at least partially, e.g., 50 cents on the dollar for the first 6 percent you save. If an employer has "frozen" the company's defined benefit plan, the company may augment the company match in the 401(k) plan to compensate for the reduced defined plan benefit.
- You get tax-deferred growth - meaning you don't pay taxes each year on capital gains, dividends, and other distributions.
- When eligible to participate, you can normally contribute more to the 401(k) than to your IRA. 
- Contributions made to a 401(k) qualify for the Retirement Savings Contributions Credit (Saver's Credit) if you meet the filing and income requirements.
- Generally not designed to allow access to funds before age 59 1/2 without paying taxes and a 10% penalty.
- Available funds are chosen by the employer; they may be better (institutional shares) but are more often worse (high-cost funds) than funds available in personal accounts. (You may have greater fund selection if the plan has a Self directed brokerage account.)
- Employer may change the fund selection at any time.
- Not insured by the Pension Benefit Guaranty Corporation (PBGC).
- Employer contributions may not become vested (i.e., become the property of the employee) until a certain number of years have passed.
Some plans offer employer stock as an investment option, and/or contribute the employer match in the form of employer stock. Plans offering employer stock must offer at least three diversified investment options with materially different risk and return characteristics. They must allow diversification of elective deferral contributions immediately (at least quarterly) and allow diversification of employer contributions after three years of service by the employee.
Keeping your 401(k) contributions in employer stock is not recommended, as you already have plenty of risk tied with the performance of your employer, and diversification or complete avoidance is strongly recommended. See, however, Net unrealized appreciation, if you hold employer stock with a low basis and you are considering a lump sum distribution rollover of plan assets.
Automatic enrollment and contributions
Employers may configure their plans to automatically enroll eligible employees, unless that employee opts out. Automatic enrollment contributions can normally be withdrawn penalty free, if requested within 90 days of the first deferral and completed within 6 months of the plan year in which they began. A safe harbor for nondiscrimination testing is available if plans have:
- Initial deferrals of at least 3% of pay, increasing annually by 1% to a number between 6% and 10% of pay,
- An employer match of 100% on the first 1% and 50% on the next 5% of pay, or
- A 3% nonelective contribution,
- 100% vesting after two years,
- Default investment selections satisfying Department of Labor regulations, and
- Annual notice to all employees regarding their right to opt out or change the automatic provisions.
Provided the notice requirement is met, and the default investments satisfy Department of Labor regulations, automatic enrollment will be governed by ERISA and preempt any contradictory state laws. 
- Contribution limits on retirement plans, including 401(k)s: IRA and 401k Contribution Limits
|Year||Under Age 50||Age 50 or Older|
|2009 - 2011||$16,500||$22,000|
- Contributions are included as wages subject to withholding for Social Security and Medicare taxes. In addition, your employer must report the elective contributions as wages subject to federal unemployment taxes.
Target retirement funds
The default option for employer provider plans is to place your contributions and employer matches into a target date retirement fund.
Empirically, investor allocation to target retirement funds has been increasing. Vanguard reports data for the employer provided funds it manages in annual 'How America Saves" studies. Among the findings:
- Employee account balance holdings of target retirement funds has increased from a 3% allocation in 2006 to a 17% allocation in 2012.
- Employee contributions to target retirement funds has increased from 4% in 2006 to 31% allocation in 2012.
- In 2012, employees 25 years old and younger held 68% of their account balances in target retirement funds.
- In 2012, employees with less than 10,000 dollars in their plans held 56% of their account balances in target retirement funds.
Employers can make certain other contributions not elected by the employees, such as profit sharing contributions. Before 2007, these contributions had to become vested on or faster than either a) 20% each year from years 3-7 of service or b) 100% after 5 years of service. Contributions made in and since 2007 must become vested on or faster than either a) 20% each year from years 2-6 of service or b) 100% after 3 years of service (with an delayed effective date for collectively bargained plans).
Under ERISA, retirement plans including 401(k) plans are not allowed to discriminate in favor of highly compensated employees. Corrections can be made by returning the excess contributions to those highly compensated employees within a specified period of time after the plan year ends. The returned funds are taxable income when received. The time period varies based on other features of the plan, generally from 2.5 to 6 months. If not returned timely by the employer, the employee will also be subject to an additional 10% excise tax.
This rule is waived for plans which meet certain safe harbors.
Early withdrawals and loans
- Hardship withdrawals, which may include withdrawals after the onset of sudden disability, money for the purchase of a first home, money for payment of higher education expenses, money for payments necessary to prevent eviction or foreclosure, and money for certain medical expenses that aren't reimbursed by your insurer. This includes hardships of your beneficiary under the plan. Conditions which determine a hardship are defined in the 401(k) plan.
- Qualified reservist distributions may be made to military reservists called up for at least 180 days, with no early withdrawal penalty. Reservists may re-contribute the amount of the qualified reservist distribution to an IRA in the 2 year period beginning the day after the end of his or her active duty.
- Most major companies also offer a loan provision on their 401(k) plans that allow you to borrow against your account and repay yourself with interest. Restrictions will vary by company but most let you withdraw no more than 50 percent of your vested account value as a loan. You then repay the loan with interest, through deductions taken directly from your paychecks. The loan must be repaid within 5 years unless it is used to buy your main home.
- Prior to tax year 2018, you had a 60-day window on employment termination, to repay a 401(k) loan balance or rollover the loan balance to an eligible retirement account, in order to avoid the loan balance from being treated as a distribution. The 2017 tax reform (Tax Cuts and Jobs Act), extended the loan repayment and rollover window to the tax filing deadline (including the tax filing extension, if applicable) for tax years 2018 and later. Effectively, this increases the time that you have, to repay or rollover the loan balance.  
- The extension of the repayment and rollover window is applicable to 403(b) and 457(b) plans, in addition to 401(k) plans.
- Most distributions (both periodic payments and lump-sum payments) from qualified retirement plans, including 401(k)'s, made to you before you reach age 59½ are subject to an additional tax of 10%. This tax applies to the part of the distribution that you must include in gross income. The additional tax does not apply if:
- The distribution is made as part of a series of substantially equal periodic payments (made at least annually) for your life (or life expectancy.
- The distribution is made because you are totally and permanently disabled.
- The distribution is made after the death of the original 401(k) owner.
However, distributions from your workplace savings plan are not subject to the 10% early withdrawal penalty if you are age 55 or over when you separate from service with your employer.
The information below on 401(k) rollovers applies in general to a rollover of a 403(b), a 457(b) or a Thrift Savings Plan as well, although each of those account types has some additional nuances. See the linked pages for each of these account types for rollover considerations specific to that type of account.
When your employment ends, you have the following options with the 401(k) at your previous employer:
- Leave your 401(k) money where it is
- Move it to your new 401(k) if you take a new job
- Move it into a 401(k) at another former employer, if the plan accepts them from separated employees (a variation of the preceding option)
- Move it into an IRA, which is called a rollover
- Take a distribution
|[The IRA rollover market] is fraught with risks for you. You could pick the wrong product, pay too much in fees, or needlessly give up a standout 401(k)—all of which could add up to a less comfortable retirement.|
|—Ian Salisbury in Why is rolling over my 401(k) such a big deal?, Money magazine, July 2014.|
If your 401(k) contains a large amount of your savings, then this decision can be very important. Some decisions can be irreversible and the investor should take great care to make the best decision. The following articles may help inform your decision:
- Why is rolling over my 401(k) such a big deal? by Ian Salisbury in Money magazine, July 2014.
- 401k Rollover: Where, Why, and How by Mike Piper at The Oblivious Investor blog, 2 April 2013
- The pros and cons of rolling over a 401(k) to an IRA - MarketWatch, 14 Jan 2014
|With a tsunami of retirees an entire industry is poised to capture rollovers. With so many juicy targets of opportunity, it shouldn’t surprise you that abuses happen.|
|—Frank Armstrong III in Pitfalls Of The 401(k) Rollover|
Consistent with Bogleheads® investment philosophy, if you are thinking of rolling over your 401(k), do not do any of the following listed below. If you are feeling pressure from a sales agent to make a decision, then wait. Pose any questions in Investing - Help with Personal Investments Bogleheads® forum. The following are several of the most common inappropriate investments sold to unwitting investors:
- Pay a front-end or back-end sales load, also known as a commission, to purchase mutual funds.
- Purchase any complicated products like a variable annuity.
- Purchase any complicated products like private REITs or other proprietary investments.
- Purchase any products with a surrender charge.
The sub-sections that follow outline some of the advantages and disadvantages with the four options described above. Note that there isn't always a single best option, meaning that the advantages of one option can be the disadvantages of an alternate option, and vice versa. An investor who is torn between different options may choose to split the difference, e.g. roll over some money to an IRA and some to a new 401(k). Many of the comparative advantages and disadvantages are simply inherent to IRAs and 401(k)s in general, so an investor considering these choices should throughly understand the characteristics of each type of plan; this section attempts to look at these considerations more specifically in the context of a 401(k) participant who is presented with the option of rolling over his or her 401(k) balance.
Leave with employer
If you change jobs and decide to leave your 401(k) with a former employer, there may be unforeseen circumstances which will result in difficulties obtaining your funds at a later time. For example, the company may go out of business, be resold, or not keep adequate records. While you are legally entitled to your funds, the practicality of these unplanned situations can result significant delays or nonpayment. For these reasons, many people strongly recommended to not leave your 401(k) money with a former employer.
That being said, if you have a high-quality and low-expense 401(k) plan, there is a case to be made to keep your assets in the 401(k) plan rather than rolling it over to an IRA or to the 401(k) plan of your new employer, if that plan is inferior to your previous plan. An investor with little investing knowledge might be better off keeping their assets in such a plan compared to the many mistakes he or she could make by rolling it over to inappropriate investments. Some plans also have unique funds (such as a Stable Value Fund) or ultra-low institutional share classes that are not available to ordinary retail investors.
However, after leaving the employer if your vested balance is below $5,000 then the employer may distribute the account either to you or a rollover IRA account in your name, provided adequate notice is given. This rule about balances below $5,000 applies at all times, not just at the time you leave the employer.
- If the 401(k) plan at a new employer is inferior to your former employer's plan, then you might be better off keeping your asset in the old 401(k) plan
- May preserve the option to do a Backdoor Roth IRA for higher income individuals, assuming the 401(k) is not a Roth 401(k)
- Asset protection can be better in ERISA plans like a 401(k) than in an IRA
- If you are retiring and are 55 years old or older, then you can withdraw from the 401(k) without paying the 10% early withdrawal payment that normally applies to withdrawals made before age 59.5.
- Concerns about control over your assets, described above
- Separated employees may have fewer options with their 401(k) plan (such as the ability to roll in funds) compared with current employees
Move to new 401(k)
If you move to a new job, you can roll over the 401(k) from your previous job, assuming the new employer's plan accepts rollovers (most do, as plans want to increase assets).
An uncommon variation of this option is to roll your assets into a 401(k) account from a different former employer, if that former employer's plan accepts rollovers from separated employes (few plans do; one that does is the Federal government's Thrift Savings Plan).
- May clear the way to do a Backdoor Roth IRA for higher income individuals, assuming the 401(k) is not a Roth 401(k)
- Asset protection can be better in ERISA plans like a 401(k) than in an IRA
- For individuals with simpler portfolios, having all one's assets in a single plan can be easier to manage
- If you are age 70.5 or older, then assets held in a 401(k) plan held where you are actively employed are exempt from Required Minimum Distribution; if the 401(k) is left at the former employer or rolled over to an IRA, then those assets are subject to RMD.
- Likely to have inferior and limited fund options than what you could access in an IRA
Rollover to IRA
- Access to better and cheaper fund options than with most (but not all) 401(k) plans
- Ability to do Roth IRA conversions, if the 401(k) plan does not allow direct conversions to a Roth IRA (some plans do).
- May impede ability to do a Backdoor Roth IRA for higher income individuals, assuming the 401(k) is not a Roth 401(k)
- Asset protection can be better in ERISA plans like a 401(k) than in an IRA
- Unsophisticated investors can be manipulated into purchasing inappropriate investments by self-interested brokers, whereas in a 401(k) plan, even an expensive one, participants typically have some protection from poor investment choices.
- If you are retiring and are 55 years old or older, the IRS allows you to withdraw from the 401(k) without paying the 10% early withdrawal payment that normally applies to withdrawals made before age 59.5. Although the IRS allows partial withdrawals, the 401(k) plan itself may allow only full withdrawals. If you rollover the assets to an IRA, then you cannot withdraw penalty-free until age 59.5.
You can take a distribution from the 401(k). This is usually advisable only if you need the money immediately. Not only will you forfeit growth on the tax-advantaged amount, but you will pay taxes on the distribution. There may also be a 10% penalty if you are under age 59.5, unless the 401(k) is with an employer from whom you retired in or after the year you reached age 55.
An in-service distribution, also known as a in-service withdrawal or in-service rollover, is when a participant takes a rollover distribution from the plan while still employed at the company that is offering the plan.
Per IRS rules this is not permitted for employees age 59.5 or younger, for their elective employee pretax or Roth contributions; for participants age 59.5 or older, a plan may allow it. A plan may, however, allow for in-service distributions of the employer matching contributions and of the employee's after-tax 401(k) contributions.
Should you die, your designated beneficiaries may rollover their inherited balance to an IRA, which will be treated as an inherited IRA.
If the designated beneficiary stays in the plan, successor beneficiaries of the designated beneficiary may not rollover an inherited balance to an IRA, per Sec 402(c)(11). A 401(k) plan may, however, choose to allow successor beneficiaries to stay in the plan, and take required minimum distribution requirements using the same schedule that the original designated beneficiary was using.
Required Minimum Distributions
An account owner must begin making distributions from the accounts at least no later than the year after the year the account owner turns 70½ unless the account owner is still employed at the company sponsoring the 401(k) plan. The amount of the distribution is based on life expectancy according to the relevant factors from the appropriate IRS tables. The only exception to minimum distribution are for people still working once they reach that age, and the exception only applies to the current plan they are participating in. A penalty is applied to anyone failing to make the minimum distribution. The penalty is 50% of the amount that should have been distributed.
An employer may also elect to make Roth 401(k) contributions available. They are the 401(k) equivalent of Roth IRA contributions, and if the 401(k) is rolled over they can be rolled directly to a Roth IRA or another Roth 401(k). These are normally administered as a sub-account of the employee's 401(k) account. Both Roth and regular contributions are subject to the same contribution limit. Whether an employee is contributing regular or Roth 401(k) funds may not influence the employer match, which must be made to the regular contribution sub-account. .
An employer may also elect to make after-tax 401 (k) contributions available. These are the 401(k) equivalent of non-deductible traditional IRA contributions, and if the 401(k) is rolled over they can be rolled directly to a Roth IRA. These are normally administered as a sub-account of the employee's 401(k) account. The limit to after-tax contributions is significantly higher than the elective deferrals limit. IRC Section 415(c)(1)(A) sets the total contribution limit for both employee and employer contributions to a 401(k), and is summarized in Overall limit on contributions. Therefore, the after-tax contribution limit for an individual is the remaining amount allowed after all employee and employer contributions. And for most individuals that can afford to contribute, it would allow them to save nearly twice as much money in tax-advantaged space as the combination of elective deferrals and employer contributions.
Just like non-deductible traditional IRA contributions, earnings are taxed upon withdraw or conversion. Therefore, to minimize the tax on gains, it is preferable to make after-tax contributions in a plan that also allows regular in-service distributions. If the after-tax contributions are rolled directly to a Roth IRA immediately (or regularly), the gains -and taxes- will be minimal.
Although 401(k) plans that allow both after-tax contributions and in-service distributions of those contributions are rare, there is the potential to greatly increase yearly contributions to a Roth IRA indirectly -well beyond the yearly Roth IRA contribution limits.
Expensive or mediocre choices
Even in a bad 401(k), you should contribute up to the company match. Choose the lowest-cost funds; many bad 401(k)'s have a few lower-cost funds. If you are eligible, additional contributions should usually go into a Roth or Traditional IRA. But unless your 401(k) is very bad and you expect to stay a very long time with the same employer, investing unmatched money in the 401(k) is likely to be better than taxable investing, because you can roll over your 401(k) to a low-cost IRA when you leave.
A reasonable rule-of-thumb is to consider investing in a taxable account if the product of the extra costs and the number of years you will stay in the plan exceeds one and a half times your combined federal and state tax rates on qualified dividends over your working career. That is, if you pay 1.70% expenses rather than 0.20%, and you pay 15% federal tax on qualified dividends, plus 5% state tax, you should still invest in the plan unless you are reasonably certain that you will stay with the employer for more than 20 years for a net loss of 30% (actually 26% because of compounding). If you pay no state tax, you should still invest in the plan unless you are reasonably certain you will stay more than 15 years.
The reason for the rule of thumb is that a long-term investment, even in a tax-efficient stock fund, is likely to lose more than your tax rate to taxes. You will pay tax every year on the dividends, continue to pay that tax after you leave the employer, and then pay capital-gains tax on most of the investment value when you sell the fund over the course of your retirement. (And if you retire in a 15% tax bracket and thus pay no capital gains on the fund sale, the lower tax bracket will also reduce the tax due on withdrawals from a 401(K), for a comparable tax savings.) [note 1]
Now, before you consider forgoing your 401(k), you may want to talk to the human resources department to see if they can improve the 401(k) plan. You may want to suggest a low-cost plan like Employee Fiduciary. You can find a sample letter to the human resources department at 401k links and suggestions. Keep in mind that the employer likely cares more about the cost of running the 401(k) plan than the expense ratios that the employees have to live with. For this reason, it is not a good idea to stress the problem with the expense ratios too much. (See How to campaign for a better 401(k) plan for more details, as well as Alternatives to a High Cost 401k Or 403b Plan for more guidance).
Involuntary cash out distributions
A defined contribution plan may involuntarily cash out, also described as force out, the accounts of ex-employee participants with a balance of $5,000 or less.
If the balances is between $1,000 and $5,000, then the employer must notify the participant and must provide for the automatic rollover to an IRA or annuity, unless the participant chooses otherwise. Balances of less than $1,000 may be distributed as cash/check to the participant; this will result in an early withdrawal penalty and a taxable event.
A 401(k) plan is not required to make these distributions, but they may, and many plans do so to reduce administrative costs of running the plans. Therefore, people with 401(k) balances of $5,000 or less with former employers should know the rules of their former plan(s) so they may manage their accounts successfully. People with balances of $1,000 or less must take extra care to monitor their account to ensure they don't have their accounts cashed out.
The best way to ensure a small-balance account is handled according to your investment goals is to roll the balance over to an IRA or to a new defined contribution plan (if applicable and if the plan accepts rollovers).
Investment policy statements
Employers are expected to have investment policy statements for the plan, governing the process by which investment selections are chosen and monitored on an ongoing basis.
Timing of contributions
Contributions deferred from an employee's pay must be contributed to the 401(k) plan and allocated to your account "as of the earliest date" the deferrals can be segregated from the employer's assets. According to Department of Labor regulation 2510.3-102, the "earliest date" is the earlier of 1) the first date reasonably practicable on an ongoing basis based on the routine processing of the payroll information, transmittal of data to the plan provider and processing by the provider or 2) the 15th business day of the month following the month in which the contribution was withheld from the employee's pay. Employers are violating ERISA and subject to 15% tax on the deemed interest when failing to contribute timely.
Plan financial reports
Plan financial reports are filed on form 5500, 5500-C or 5500-R. Some of the information from these reports must be made available to employees, often on the company intranet.
- Alternatives to a High Cost 401k Or 403b Plan at TheFinanceBuff.com contains a spreadsheet which can be used to compare alternatives for your situation (July 23, 2008). The spreadsheet approximately agrees with the rule-of-thumb estimates for the common situation in which you have 20-30 years with the employer and then average about another 10 years in retirement.
- section 401(k) of the Internal Revenue Code
- EBRI Notes, October, 2011, Vol. 32, No. 10.
- 401(k) Resource Guide - Plan Participants - Limitation on Elective Deferrals
- Retirement Savings Contributions Credit (Saver's Credit), Publication 571, IRS
- See Automatic enrollment: Benefits and costs of adoption
- Historical data: Retirement Plan Limits, from Money Alert. 2020: IRS announcement of 2021 pension limits, from the IRS.
- Topic 424 - 401(k) Plans, from the IRS, viewed June 19, 2015.
- How America Saves 2013, Vanguard Institutional
- Retirement Plans FAQs regarding Hardship Distributions, from the IRS.
- 401(k) Resource Guide - Plan Participants - General Distribution Rules, from the IRS
- Recent Changes in Tax Laws Affect Qualified Retirement Plans and Health & Welfare Benefits, Fidelity.
- Tax reform gives some 401(k) borrowers more time to repay, Credit Karma.
- 401k Vesting Dispute - Need Advice Bogleheads.org forum discussion, Jul 09, 2010
- "The One Retirement Move You Must Get Right", Money Magazine, July 2014, pp. 45-52, by Ian Salisbury.
- Just retired...any reason to move 401K to IRA? in Bogleheads.org forum, July 4, 2014.
- Retirees Suffer as $300 Billion 401(k) Rollover Boom Enriches Brokers by John Hechinger at Bloomberg.com, Jun 17, 2014 5:37 PM ET
- Is this retirement move right for you? by Melanie Hicken in money.cnn.com, July 18, 2014: 6:52 AM ET
- IRS Topic 558
- In-Service Withdrawal: The Law and The Plan Rules at The Finance Buff, February 1, 2011
- Bogleheads • View topic - In-service 401k rollover to IRA (under 40, still employed) Feb. 27, 2010
- Bogleheads® forum post: , Alan S. 4 Oct 2014
- See Roth 401(k) Investing Guide
- Employee Fiduciary
- IRS Pub 560
- See Regulatory Brief: Update on Plan Fee Disclosure for recent regulatory actions
- IRS IRC 401(k) Plans
- The Hewitt 401(k) Index™ Observations
- 401(k) Plans For Small Businesses
- History of 401(k) Plans
- IRS Publication 575, Pension and Annuity Income
- FINRA Smart 40(k) Investing
- 401(k) Links and Suggestions (forum post)
- Setting up a 401(K) plan, (forum post)
- Bogleheads® forum topic: , 20 August 2015.