401(k) Calculator: What Your Balance Could Be, as an Honest Range
Nobody can tell you what your 401(k) will be worth, because nobody knows future returns. What you can know is a realistic range. This calculator runs 2,000 possible market histories in today’s dollars, with 2026 contribution limits and fees, and shows the middle outcome alongside the bad and good ones.
On this page
Project your balance
Everything is in today’s dollars. We run 2,000 possible market histories instead of one steady rate. Stocks are assumed to return 5% a year after inflation on a typical long run, with year-to-year swings of about 17%; bonds 1.5%, with swings of about 6%. Those are assumptions, not forecasts, and real markets have had worse stretches than a model produces. Contributions stop at the 2026 limits (IRC §402(g), §414(v), §415(c)), assumed to rise with inflation. The range shows 1-in-10 bad and good outcomes; it isn’t the worst or best that can happen.
A worked example
These are the calculator’s starting numbers. You’re 35 with $50,000 saved, earn $75,000, contribute 10% of pay, and get 4% from your employer. The money is in a target-date fund with fees of 0.5% a year, and your pay rises 1% a year faster than inflation.
| You and your employer put in | $415,000 |
| Bad markets: 1 history in 10 ends below | $470,000 |
| Middle outcome | $800,000 |
| Good markets: 1 history in 10 ends above | $1,540,000 |
| A steady 7% a year with no fees would say | $1,520,000 |
The steady-7% answer is higher than 89% of the simulated outcomes. That’s the problem with a single compound-growth line: it assumes the good case and hides how wide the range really is.
Why a range instead of one number
Two savers with identical habits can retire with very different balances, because of when good and bad years happened to fall. A calculator that uses one steady rate can’t show that. Running many possible histories does, and the spread between the bad and good outcomes is the honest measure of what you don’t know.
The range is about markets, not a promise. One outcome in ten is below the bad-markets figure, and history has had stretches worse than any model produces. It’s a planning tool, not a forecast.
What moves the result most
- Your contribution rate. Every percentage point of pay adds to every outcome, bad markets included. Returns can’t be controlled; this can.
- The whole match. Missing part of your employer’s match is money that never compounds. The match calculator checks you get all of it.
- Fees. Try 0.2% against 1% in the options. Over 30 years, the gap is often six figures.
- Time. Retiring two years later adds two years of contributions and growth, and two fewer years of withdrawals.
Frequently asked questions
What rate of return should I use for my 401(k)?
This calculator doesn’t ask you for one. It assumes stocks return about 5% a year after inflation over a typical long run and bonds about 1.5%, with realistic year-to-year swings. If you use a single-rate calculator, 4% to 5% after inflation for a stock-heavy mix is a more careful input than the 7% or 10% often quoted.
How much will my 401(k) pay me each year in retirement?
A common rule of thumb is 4% of the balance in the first year, adjusted for inflation after that. At the middle outcome in the example, that’s about $32,000 a year before tax. The calculator shows it for your own range.
Does the calculator include the contribution limits?
Yes. Your contributions stop at the 2026 limit of $24,500, or more with catch-up from age 50, and employer money stays inside the $72,000 total limit. The limits are assumed to rise with inflation, so they stay constant in today’s dollars.
Related reading
Sources: IRS Notice 2025-67 (2026 limits) · IRC §402(g) · IRC §415(c)