Enter what you have saved already, what you can add each month, an assumed yearly return and how long the money stays invested, and this calculator shows the future value, how much of it is money you put in, and how much is growth — with a year-by-year table so you can watch the compounding build. There is no sign-up and nothing to submit — the results update as you type.
The return you enter is an assumption for the estimate, not a promised or typical return. Real investments go up and down.
after 10 years
starting amount + contributions
future value minus what you put in
| Year | Total contributed | Balance at year end | Growth earned |
|---|---|---|---|
| 1 | $12,400.00 | $13,201.42 | $801.42 |
| 2 | $14,800.00 | $16,634.27 | $1,834.27 |
| 3 | $17,200.00 | $20,315.28 | $3,115.28 |
| 4 | $19,600.00 | $24,262.39 | $4,662.39 |
| 5 | $22,000.00 | $28,494.83 | $6,494.83 |
| 6 | $24,400.00 | $33,033.24 | $8,633.24 |
| 7 | $26,800.00 | $37,899.74 | $11,099.74 |
| 8 | $29,200.00 | $43,118.03 | $13,918.03 |
| 9 | $31,600.00 | $48,713.55 | $17,113.55 |
| 10 | $34,000.00 | $54,713.58 | $20,713.58 |
How the estimate works: in monthly mode the balance grows each month at one twelfth of the annual return you enter, then your monthly contribution is added at the end of the month. In annual mode growth is applied once a year and a full year of contributions is added at year end. The return is a steady assumption you choose — real markets do not grow in a straight line, returns vary year to year, and taxes, fees and inflation are not included.
How to use this calculator
- Enter your starting amount — what is already in the account today. Leave it at zero if you are starting from scratch.
- Add the monthly contribution you can realistically keep up.
- Set an assumed annual return. This is a test assumption, not a promised return.
- Choose how many years the money stays invested, and monthly or annual compounding.
- Read the future value, total contributed and growth earned, then scan the year-by-year table to see when growth starts to overtake contributions.
How compounding does the heavy lifting
With simple interest, growth is paid only on the amount you started with, so the balance climbs by the same amount every year. With compound interest, each period's growth is added to the balance and the next period's growth is calculated on the bigger total. Early on the difference looks tiny, which is why compounding feels disappointing in year one. Given enough years, the growth-on-growth part becomes the largest part of the balance — time in the account does more work than any single contribution.
That is also why the return assumption matters so much, and why this tool asks you to choose it. A higher assumed return does not just add a little more each year — it compounds too. Run your plan at two or three different returns before drawing any conclusion from the headline figure.
A worked example
Start with $10,000 at 7% for 10 years, with no monthly contributions and annual compounding, and the balance reaches $19,671.51 — the original $10,000 plus $9,671.51 of growth. Now keep the same starting amount, rate and timeframe, switch to monthly compounding and add $200 a month: the balance reaches $54,713.58. Of that, $34,000 is money you put in ($10,000 at the start plus $24,000 of contributions) and $20,713.58 is growth. The contributions more than double the ending balance, and the growth is larger than in the first example because there was more money in the account for compounding to work on.
Monthly vs annual compounding, in plain terms
Monthly compounding credits growth twelve times a year, so each month's growth starts earning its own growth the following month. Annual compounding credits it once, at year end. Savings accounts and most investments effectively compound more often than once a year, while the annual setting is handy for checking the textbook formula by hand. Either way, the inputs that usually change the answer most are the number of years and the monthly contribution — not the compounding setting.
More calculators & tools
Planning specifically for life after work? The Retirement Calculator adds ages and an employer 401(k) match on top of the same maths. Comparing a savings account with a fixed rate and a set term? Try the CD Calculator. Checking the other side of the ledger, what borrowing costs? Use the Loan Calculator. Every tool sits on the calculators hub, our guide to building income over time covers the habits behind the numbers, and the budgeting guides show how to find the monthly contribution in the first place.
This calculator provides estimates for general education only and is not financial, legal, or tax advice. Results use the figures you enter and standard compound growth maths with a steady assumed return; real returns vary, can be negative, and are reduced by taxes, fees and inflation, so treat the output as a comparison tool, not a forecast. For advice about your own situation, talk to a qualified professional.
Frequently Asked Questions
What is compound interest?+
It is growth on growth. Each period, the return is calculated on everything in the account — your original money, any contributions, and all the growth earned so far — rather than only on the amount you first put in. Over long periods that snowball effect is why starting early usually matters more than starting with a larger amount.
What is the difference between monthly and annual compounding?+
Monthly compounding applies one twelfth of the yearly return every month, so growth itself starts earning growth sooner. Annual compounding applies the full yearly return once a year. With the same yearly rate and the same contributions, monthly compounding ends slightly ahead — the gap is small over a few years and larger over decades.
How much difference do monthly contributions make?+
Often more than the starting amount. A contribution made every month adds new money for compounding to work on, and the earlier contributions have the longest time to grow. Use the year-by-year table above to compare your plan with contributions set to zero against the same plan with your monthly amount included.
What return should I enter?+
Enter a cautious assumption you want to test, not a figure you expect to be guaranteed. Investments do not grow in a straight line — returns vary, some years are negative, and fees and taxes reduce what you keep. Trying the same plan at a lower return, such as 2 or 3 points lower, shows how much the answer depends on that one assumption.
Does this calculator include taxes, fees or inflation?+
No. It shows growth before taxes, fund and account fees, and inflation. Your real outcome will be lower once those are counted, and inflation means the future amount buys less than the same amount buys today. Treat the result as a way to compare plans, not as a forecast of what you will have.
Does this calculator store or send my data?+
No. The calculator runs entirely in your browser. Nothing you type is sent to a server, saved, or shared — refresh the page and it is gone.