Tool · Money
Put in what you've got saved, what you'll add each month and a growth rate, and the calculator shows what the money becomes over the years you pick — and how much of the ending figure is yours and how much is growth.
Where does each number come from?
- Starting balance
- Whatever’s already in the account today — the balance on your latest statement or in the app. Zero works, and then the calculator shows what the monthly habit builds on its own.
- Monthly contribution
- What you’ll add each month, counted at the end of the month. There’s a box in the panel for a yearly raise to it, for anyone whose contribution goes up when their pay does.
- Yearly growth
- The rate the money earns, held at the same number every year. The box starts at what the U.S. government pays to borrow for ten years, because that’s a published rate with a date on it and not anybody’s guess about the stock market. A savings account, a bond fund and a stock fund each earn something different, and the rate you type is the whole difference.
- Years
- How long the money sits. The last row of the table is the number the headline shows.
What moves the answer?
Let’s say you start with $1,000 and add $100 a month for twenty years. At 5% a year that comes to about $44,000, and $25,000 of it is money you put in. At 8% it’s about $64,000 on the same deposits. The extra three points are worth about $20,000 over twenty years, and every dollar of that difference is growth, since your deposits didn’t change.
Time does as much as the rate does. The same $100 a month for thirty years at 5% is about $88,000 — double the twenty-year figure for half again as many deposits. The year the table marks is the one where a year’s growth first outruns a year’s deposits; after that the account is adding more to itself than you are.
What does the calculator take as given?
- The growth rate
- Starts at 5.01%, the yield on the ten-year U.S. Treasury note on 18 September 2026, from the Federal Reserve’s daily rates release. It changes every business day, and the calculator holds whatever you type flat for the whole run.
- How growth is added
- Monthly, on the balance at the start of the month, with quarterly and yearly as options in the panel. Your contribution lands at the end of each month.
- The watch line
- If your yearly contributions pass what a 401(k) or an IRA lets you put in for 2026 — $24,500 of your own pay into a 401(k), $7,500 into an IRA, from the IRS’s November 2025 notice — a line appears saying so. It doesn’t stop the math.
- What's left out
- Tax, both inside the account and when you take the money out. Fund fees. Inflation, which makes a dollar thirty years from now buy less than one today. And the fact that real returns arrive as a different number every year — two accounts with the same average can end in different places.
The thousand dollars and the hundred a month are starting figures to make the math easy to follow; your own balance, your own rate and how long you leave it are on your statement and in your plans, and those three set your number.
Sources
- Federal Reserve, Statistical Release H.15, Selected Interest Rates — 10-year Treasury constant maturity, 5.01% on 18 September 2026, release of 21 September 2026.
- Internal Revenue Service, Notice 2025-67 (13 November 2025) — 2026 employee deferral limit $24,500; IRA contribution limit $7,500.
- Bills & Beans, The Money Numbers That Change Every January — both figures with their quotes and dates.