How this calculator works
The deterministic simulation grows the remaining balance at the monthly assumed rate and applies the selected withdrawal at the beginning or end of each period. The reverse solver uses the corresponding annuity relationship.
Formula
balance[m] = balance[m-1] × (1+r) - withdrawalDeterministic monthly withdrawal simulation; withdrawal timing controls whether cash is removed before or after monthly growth.
Worked example
$500,000 corpus, $5,000 monthly withdrawal, 8% estimated annual return for 5 years is a verified test case used by the calculation engine.
Assumptions and limitations
- Return is constant and converted to a monthly periodic rate.
- Withdrawals are level monthly amounts.
- Taxes, fees, volatility and sequence-of-returns risk are not modeled, so the reverse result is a mathematical level withdrawal rather than a guarantee of real-world sustainability.
Methodology & sources
This calculator uses deterministic, versioned calculation logic. The formula and verified examples above are part of the calculation definition used by CalcuMint.
Frequently asked questions
Does sustainable withdrawal mean guaranteed retirement income?
No. It is the level withdrawal that mathematically amortizes the modeled corpus under the stated constant-return assumptions.
Can the modeled corpus be depleted before the selected term?
Yes. The simulation reports depletion when withdrawals exhaust the modeled corpus under the selected return and timing assumptions.