# Difference between revisions of "Amortization based withdrawal formulas"

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A=\operatorname{PMT}(\frac{1+r}{1+g}-1,n,-P,\frac{B}{(1+g)^n},1) | A=\operatorname{PMT}(\frac{1+r}{1+g}-1,n,-P,\frac{B}{(1+g)^n},1) | ||

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+ | ==External links== | ||

+ | *{{Forum post|t = 274243| title = Using the Time Value of Money Formula to Determine Withdrawals: Year 2000 Retiree Example | author = willthrill81, date = February 27, 2019}} |

## Revision as of 02:15, 5 November 2020

This article or section is in the process of an expansion or major restructuring. You are welcome to assist in its construction by editing it as well. |

Contributor note: Comments are being solicited in this Bogleheads® forum topic: Using the Time Value of Money Formula to Determine Withdrawals: Year 2000 Retiree Example |

These are the formulas for Amortization Based Withdrawal (ABW).

## Amortization Formula

If is the lump sum value, is the amount paid over periods, and is the interest rate, then

Note that this formula assumes that the periodic payment begins next period, not immediately. The lump sum is the value today (period 0), and the periodic payments are being made in periods 1 through . This is natural in the context of a loan: the loan is taken out today and the repayments only start next period.

The formula does not work for . You can input close to zero in the above formula to get an approximate answer. Or you can use simple division to get the exact answer.

In Excel, the PMT function can be used for this calculation:

## Amortization Based Withdrawal Formula

To calculate portfolio withdrawals, set current portfolio value, number of years over which withdrawals are to be spread out, and expected return of the portfolio.

The amortization formula above assumes that payments begin next year, not immediately. If withdrawals are to start this year, the formula needs to be divided by :

In Excel, the PMT function can be used for this calculation:

## Adding a Terminal Balance

Instead of fully depleting the portfolio, the amortization can be modified to leave behind a terminal balance. If the target terminal balance is dollars, withdrawal is:

In Excel, the PMT function can be used for this calculation:

## Allowing for Rising or Falling Withdrawal Schedules

Instead of a constant withdrawal schedule, the amortization can be modified to generate a withdrawal schedule that grows at a rate of per year.

generates a rising withdrawal schedule, generates a declining withdrawal schedule, and generates a constant withdrawal schedule.

The formula does not work for . You can input close to in the above formula to get an approximate answer. Or you can use simple division to get the exact answer.

In Excel, the PMT function can be used for this calculation:

## External links

- Bogleheads® forum topic: Using the Time Value of Money Formula to Determine Withdrawals: Year 2000 Retiree Example, willthrill81, date = February 27, 2019