Retirement Spending Calculator: See How Long Your Savings Will Last

Step 1: Your spending goal gets adjusted for inflation

The monthly budget you enter is in today’s dollars. Prices typically rise over time, so the same monthly budget will cost more by the time you actually retire. This step accounts for that:

Future Monthly Spending = Monthly Spending × (1 + Inflation Rate) raised to the power of Years to Retirement

For example, if retirement is 10 years away, your target is $4,000 a month today, and inflation runs at 3% a year, that $4,000 becomes roughly $5,375 a month by the time you retire.

Step 2: Social Security gets the same adjustment

Your expected Social Security benefit is also entered in today’s dollars, so it’s adjusted the same way:

Future Monthly Social Security = Monthly Social Security × (1 + Inflation Rate) raised to the power of Years to Retirement

A $2,000 a month benefit today becomes roughly $2,687 a month after that same 10-year period.

Step 3: Social Security is subtracted from spending

Net Monthly Need = Future Monthly Spending − Future Monthly Social Security

Using the numbers above, $5,375 minus $2,687 leaves about $2,688 a month.

The reasoning here: Social Security income arrives every month and covers part of your expenses before savings are touched. In practice, a Social Security deposit goes toward regular costs like rent, groceries, or bills first. Savings only need to cover what’s left after that. So the calculator doesn’t assume savings have to produce the full $5,375 a month, only the $2,688 that Social Security doesn’t already cover.

Step 4: Current savings continue growing until retirement

Savings don’t sit idle. They earn a return each year between now and retirement, the same way they would in an actual investment account:

Balance at Retirement = Current Savings × (1 + Return Rate) raised to the power of Years to Retirement

$500,000 growing at 5% a year for 10 years comes out to roughly $814,000 by the time retirement starts.

Step 5: Retirement is simulated month by month

Starting the month retirement begins, the calculation moves forward one month at a time. Each month, the balance earns a small return, then that month’s spending is withdrawn. Once a year, both the spending amount and the Social Security benefit increase to keep pace with inflation, since prices continue rising after retirement starts too. This continues through to the planning age you specified.

Step 6: The result shows where things stand

If the balance is still positive once it reaches your planning age, the result shows in green, indicating your savings held up, along with roughly how much would be left over. If the balance runs out earlier, the result shows in red, with an estimate of when that happens.

One thing to keep in mind

This calculator applies a single steady investment return and a single steady inflation rate across every year. Real markets fluctuate, and inflation isn’t perfectly consistent either. Treat this as a planning estimate rather than a guarantee, and use it to see how the numbers shift as you adjust things like retirement age, monthly spending, or your planning age.