About this tool
Withdrawal / Annuity Payout Calculator (SWP) is a free, in-browser tool that models fixed monthly withdrawals from a lump sum that keeps earning returns — a systematic withdrawal plan, annuity payout, or simply "how long will my savings last". Everything runs locally in your browser.
It solves whichever variable you need: how long the corpus lasts at a given withdrawal (n = −ln(1 − PV·i/W)/ln(1+i)), the sustainable monthly payout for a chosen number of years (W = PV·i/(1 − (1+i)^−n)), or the final balance after a period of withdrawals. The rate is annual, compounded monthly (÷ 12), with interest credited before each withdrawal, and a year-by-year table shows withdrawals, interest earned and the running balance.
Use it to plan retirement drawdown: for example, how long 500,000 lasts at 3,500 a month with 6% returns, or the payout that exactly exhausts it over 20 years.
Frequently asked questions
Why does the duration show infinity sometimes?
If the monthly withdrawal is no larger than the monthly interest on the corpus (W ≤ PV × rate/12), the balance never falls — interest alone funds the payout, so the money lasts indefinitely. The table then previews the first 30 years of the growing balance.
What are the timing conventions?
The annual rate is divided by 12 into a monthly rate; each month interest is credited first, then the withdrawal is taken at month end. The final withdrawal is reduced to whatever remains, so the balance ends exactly at zero rather than going negative.
How is the yearly table built?
The simulation runs month by month and aggregates each 12 months into one row — total withdrawn, total interest earned and the end-of-year balance — so even multi-decade plans stay readable.
Is my retirement data uploaded?
No. The full simulation and table are generated in your browser; no corpus or withdrawal figures leave your device.
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