Savings Withdrawal Calculator
How long a balance lasts at a given withdrawal rate — and the withdrawal that would make it last indefinitely.
Each period the balance earns interest and loses a withdrawal.
How the savings withdrawal calculator works
Each period the balance earns interest and loses a withdrawal. If the withdrawal exceeds the interest the balance falls, slowly at first and then faster as the interest shrinks with it.
The perpetual withdrawal — the amount the interest alone covers — is the dividing line. Below it the balance never runs out; above it, depletion is only a question of when.
Formula: n = −ln(1 − rPV/PMT) / ln(1+r)
Worked examples
| Inputs | The balance lasts | Note |
|---|---|---|
| 500k at 3,000 a month | 23 years 10 months | about 24 years |
| Within the interest | indefinitely — the interest covers the withdrawal | lasts indefinitely at 5% |
| A heavy draw | 10 years 10 months | about 11 years |
FAQFrequently asked questions
How long will my savings last?
It depends on the gap between the return and the withdrawal. This page runs the balance forward month by month.
What withdrawal is sustainable?
One the interest covers. At 5% on 500,000 that is about 2,080 a month before inflation.
Why does inflation matter so much?
Because a fixed withdrawal loses purchasing power. Indexing it keeps the real income steady and shortens how long the balance lasts, often dramatically.
Is this the 4% rule?
Related but not the same. The 4% rule is an empirical result for 30-year retirements with variable returns; this is deterministic arithmetic at a fixed rate.
What about sequence risk?
This assumes a constant return. Real markets do not oblige, and poor returns early in a withdrawal phase do disproportionate damage.
Where these figures come from
- CFA Institute — Quantitative Methods: The Time Value of Money — the discounting, annuity and IRR conventions used here
- US Federal Reserve — Regulation Z (Truth in Lending), APR calculation — why APR includes fees where a nominal rate does not
- Consumer Financial Protection Bureau — the US consumer finance regulator
Last checked: September 2026. These are the standard textbook formulas; the conventions named are those of the CFA Institute curriculum and ISO 80000 usage.