Retirement Savings Duration Calculator: Monthly Withdrawals
Estimate how long savings could fund monthly withdrawals under a constant-return scenario. Include an optional annual withdrawal increase and choose a projection horizon. This is a simplified cash-flow model, not a forecast or a guarantee that savings will last.
How savings duration is calculated
For each month, the calculator applies the modeled return to the opening balance, then deducts the scheduled withdrawal. If the remaining savings cannot cover the entire scheduled amount, the final withdrawal uses the available balance and the projection stops at depletion.
The monthly return is (1 + annual effective return / 100) raised to the power 1/12, minus 1. This converts an effective annual rate rather than simply dividing it by 12. Each monthly return is rounded to cents; negative half-cent amounts round away from zero.
Worked example with no return
Enter Starting savings 240000 and Initial monthly withdrawal 2000. Leave Annual effective return (%) and Annual withdrawal increase (%) at 0, with Projection horizon (years) 40. Select Calculate savings duration.
With no return or increase, 240000 / 2000 = 120 full monthly withdrawals. Savings are depleted in month 120, corresponding to 10 modeled years. Total withdrawn is 240000.00. This simple example does not assume any investment growth.
Annual increases and inflation
The withdrawal schedule starts with your entered monthly amount. At the beginning of each later modeled year, that amount is multiplied by (1 + annual increase / 100) raised to the number of completed years, then rounded to cents. The first increase applies to month 13.
An annual increase can represent a spending adjustment for inflation, but the tool does not forecast inflation or purchasing power. Enter a nominal return when using withdrawals that increase in nominal terms. Mixing a real, inflation-adjusted return with a separate inflation increase can count inflation twice.
What a constant return leaves out
Actual investment returns vary, and withdrawals interact with the order of gains and losses. A constant-rate model does not capture sequence-of-returns risk, volatility or the probability of running out of money. Its output is not a safe withdrawal rate recommendation.
Taxes and fees affect results only through your chosen net return or withdrawal amounts. The tool does not separately calculate them, Social Security, pensions, contributions, required distributions or irregular expenses. Model the amount needed from this savings pool, rather than assuming every retirement expense must be withdrawn from it.
Interpret the horizon correctly
If savings remain at the end, the result reports that they remain after the modeled period. It does not infer a later depletion date or promise indefinite funding. A return high enough to offset current withdrawals can still be an unrealistic or risky assumption.
The horizon is limited to 100 years. A separate numerical cap stops a scenario if the balance would exceed 10000000000000 before a withdrawal; that stop is reported as a calculation limit, not a successful lifetime plan. For accumulation rather than withdrawals, use the Compound Interest Calculator.
For a step-by-step walkthrough, read How Long Will Retirement Savings Last? Monthly Withdrawal Examples.
Input limits and privacy
Starting savings and initial withdrawal must each be greater than zero up to 1000000000, with at most two decimal places. Annual effective return may be -50 to 50 percent, annual withdrawal increase 0 to 20 percent and the horizon 1 to 100 whole years. These are software limits, not recommended financial assumptions.
Money balances use integer cents, with floating-point calculations for return and increase factors. Calculations run locally and entries are not saved or transmitted by this calculator. The hosting website may use separate analytics or advertising services.
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