Tool · Money
Type in your age, the age you're planning around, what's in your retirement account and what goes in each month, and the calculator shows what the account could hold by then, how much of it you put in yourself, and what that total would buy in today's dollars.
Where does each number come from?
- Your age now, and the age you're planning around
- The second one is yours to pick. Beside the box, the calculator prints the age Social Security calls your full retirement age for your birth year — 67 for anyone born in 1960 or later — because that’s the one published anchor, and it’s on your Social Security statement.
- What's in the account today
- The balance on your latest 401(k) or IRA statement, or in the plan’s app. If you’ve got more than one account, add them up.
- What goes in each month
- Your own contribution plus anything your employer adds. Your contribution is the retirement line on your pay stub; the employer part is the match formula in your plan’s summary plan description, and the employer match calculator turns that formula into dollars.
- Yearly growth
- The box starts at what a broad basket of large U.S. stocks averaged each year over the last fifty years, dividends included and before inflation — about twelve percent, as one university’s public dataset records it. That’s a fact about the past, and the next fifty years aren’t promised to match it. One click swaps in the ten-year Treasury yield, a government bond rate, for a plainer run.
- Expected inflation
- What prices rise by each year. The box starts at the most recent twelve-month change in the consumer price index, and it’s only used for one line — the today’s-dollars figure.
What moves the answer?
Let’s say you’re 30 with $20,000 saved, you and your employer put in $500 a month, and you’re planning around 67. At the fifty-year stock average that grows to about $5.6 million by 67, of which $242,000 is money that went in. At the Treasury rate it’s about $770,000 on the same deposits. The gap between those two is the whole argument about what a retirement account holds, and the calculator can’t settle it — it can only show you both.
The today’s-dollars line matters more here than on any other page. At 3.4% inflation for thirty-seven years, $5.6 million buys what about $1.6 million buys today, and $770,000 buys what about $220,000 does. Those are still large numbers, and they’re the ones to picture, because that’s the money you’d be spending.
What does the calculator take as given?
- The stock figure
- 11.93% a year, compounded, is what the S&P 500 returned on average from 1976 through 2025 with dividends reinvested, from the historical-returns dataset Aswath Damodaran publishes at NYU Stern, updated 5 January 2026. The simple average of the fifty yearly returns is higher, at 13.17%; the calculator uses the compounded one because that’s the rate a steady balance would have had to earn to end where the index did. Within those fifty years the index lost 37% in 2008 and gained 37% in 1995, and the average hides both.
- The Treasury alternative
- 5.01%, the ten-year Treasury yield on 18 September 2026 from the Federal Reserve’s daily release.
- Inflation
- 3.4%, the twelve-month change in the consumer price index for August 2026, from the Bureau of Labor Statistics’ release of 11 September 2026. The next release is 14 October.
- Full retirement age
- The Social Security Administration’s table: 66 for people born 1943 to 1954, rising by two months a year for 1955 through 1959, and 67 for 1960 and later.
- The contribution limits
- A line appears if your yearly contributions pass the 2026 401(k) limit of $24,500 of your own pay or the IRA limit of $7,500, from IRS Notice 2025-67.
- What's left out
- Social Security itself — your statement at ssa.gov estimates it. Pensions. Taxes when you take the money out, which differ between Roth and Traditional accounts. Fund fees, which are in your plan’s fee disclosure. And the order the good and bad years arrive in, which changes the ending balance even when the average doesn’t.
Thirty years old with twenty thousand saved is one made-up saver; your own balance is on your latest statement, your contribution is on your pay stub, and your full retirement age is on the Social Security statement you can download today.
Sources
- Aswath Damodaran, NYU Stern School of Business, Historical Returns on Stocks, Bonds and Bills: 1928–2025, updated 5 January 2026 — S&P 500 total return by year; the 1976–2025 compound average of 11.93% and arithmetic average of 13.17% are computed from the table.
- Federal Reserve, Statistical Release H.15 — 10-year Treasury constant maturity, 5.01% on 18 September 2026, release of 21 September 2026.
- U.S. Bureau of Labor Statistics, Consumer Price Index — August 2026, USDL-26-1496, released 11 September 2026 — all items up 3.4% over twelve months.
- Social Security Administration, Retirement Age and Benefit Reduction — Full Retirement and Age 62 Benefit By Year Of Birth.
- Internal Revenue Service, Notice 2025-67 (13 November 2025) — 2026 contribution limits.