How long will $600,000 last at $5,000 a month?

About 184 months, or 15.3 years, at a 6% annual return. The first month earns $3,000 of interest against a $5,000 withdrawal, so the balance shrinks from the start and the decline speeds up as it goes.

How long will my retirement money last?

It depends on the starting balance, the monthly withdrawal, and the return. This calculator uses a fixed withdrawal and a constant monthly return to estimate the number of payments before the balance hits zero.

What if I withdraw less than the monthly interest?

Under the constant-return assumption the balance lasts indefinitely, because the withdrawal never eats into principal. That's a math result, not a promise — inflation erodes the real value of a fixed withdrawal over time.

Does this account for inflation?

No. The withdrawal stays flat. If you raise withdrawals each year to keep pace with prices, the money runs out noticeably sooner.

What withdrawal makes savings last indefinitely?

Anything at or below the first month's interest, which is balance × annual return ÷ 12. For $600,000 at 6% that's $3,000 a month. The calculator shows this figure.

How does the 4% rule compare to this?

The 4% rule suggests withdrawing 4% of the starting balance in year one ($24,000 on $600,000, or $2,000 a month) and adjusting for inflation, aiming for a 30-year horizon. This calculator instead tells you how long a specific dollar withdrawal lasts.

Retirement Duration Calculator

How Long Can Retirement Savings Last?

A retirement balance can look large and still disappear quickly if withdrawals are too high. This calculator estimates the number of monthly payments available from a starting balance after applying a constant monthly return and a fixed withdrawal amount.

The result is useful for comparing scenarios. Try several withdrawal levels, reduce the expected return, and remember that inflation will usually push spending higher over time. The calculation does not model market volatility, taxes, fees, required distributions, healthcare costs, or changing spending patterns.

If the withdrawal is no greater than the interest earned in the first month, the simplified model reports an indefinite duration. That is a mathematical result, not a guarantee that the purchasing power of the account will remain intact.

How to Calculate Retirement Duration

Step One: Convert the annual return to a monthly return

Monthly withdrawals require a monthly rate.

monthly return = annual investment return / 12

6% / 12 = 0.5% per month

Step Two: Check the first month’s interest

Compare the first month’s interest with the planned withdrawal.

first month interest = startingBalance × monthly return

$600,000 × 0.005 = $3,000

Because the planned withdrawal is $5,000, it exceeds the first month’s interest and the balance declines.

Step Three: Solve for the number of payments

Use the declining-annuity duration formula, where is the monthly return:

With , , and :

Step Four: Convert months into years

Retirement Duration Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

How much the return assumption matters

The return you enter changes the answer more than most people expect. Here is the same 600,000-dollar balance and 5,000-dollar monthly withdrawal at different constant annual returns:

Annual return	Months	Years
0%	120.0	10.0
3%	142.8	11.9
4%	153.5	12.8
5%	166.7	13.9
6%	183.7	15.3
7%	207.0	17.2

Moving from 6% to 4% takes about two and a half years off the result. Because real returns vary from year to year, it’s worth running a cautious return alongside your central estimate.

Allowing for inflation

The calculator holds the withdrawal flat, so each later payment buys a little less. One simple way to allow for inflation is to enter a real return: roughly the expected return minus expected inflation. With a 6% return and 3% inflation, enter about 3%. The answer then describes withdrawals that keep their buying power, and in this example the money lasts about 11.9 years instead of 15.3.

Finding a withdrawal that doesn’t run out

The calculation turns on the first month’s interest, . Withdraw less than that and the balance never falls in this model. With 600,000 dollars at 0.5% a month, the interest is 3,000 dollars, so withdrawals at or below 3,000 dollars a month report an indefinite duration. Anything above it eats into the principal, and the larger the gap, the faster it goes.

Common mistakes

Entering the monthly return as the annual return. The calculator divides by 12 for you, so enter 6 for 6% a year, not 0.5.
Using take-home spending as the withdrawal. Withdrawals from many retirement accounts are taxed, so the gross amount you take out is usually higher than what you spend.
Ignoring other income. A pension or social security payment reduces how much the savings have to supply each month, which can lengthen the duration a lot.
Treating the result as a guarantee. A run of poor returns early in retirement shortens the real duration even when the long-term average matches.

Sources and assumptions

This calculator assumes:

The investment return is constant and compounds monthly.
Withdrawals are the same amount every month and are not adjusted for inflation.
Taxes and investment fees are not deducted.

Sources:

Compound interest calculator, U.S. Securities and Exchange Commission (Investor.gov)
Consumer Price Index (inflation data), U.S. Bureau of Labor Statistics

Figures last reviewed: 5 October 2026. Educational estimates, not professional advice.