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Compound interest calculator

See how a starting balance and monthly contributions grow over time, split between what you put in and compound growth. Change any input to recalculate instantly.

Free market tools, live on StockMarketCap

We track 5,000+ stocks across 20 global markets with live prices, rankings, and fundamentals. No account needed to explore.

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$
$
%
yr
Interest applied every month
Ending balance after 20 years
$300,851
$130,000 invested grows by $170,851 at 7% a year
You put in$130,000
Compound growth$170,851
Total invested
$130,000
Growth earned
$170,851
Return multiple
2.31x
Time horizon
20 years
See what the market has actually returned across 5,000+ stocks
Balance growth over timeTotal value vs contributions
$0$75,213$150,425$225,638$300,851Now5y10y15y20y
Year by yearMonthly compounding
YearContributedGrowthBalance
1$16,000$919$16,919.19
2$22,000$2,339$24,338.58
3$28,000$4,294$32,294.31
4$34,000$6,825$40,825.16
5$40,000$9,973$49,972.70
6$46,000$13,782$59,781.53
7$52,000$18,299$70,299.43
8$58,000$23,578$81,577.68
9$64,000$29,671$93,671.22
10$70,000$36,639$106,639.02
11$76,000$44,544$120,544.25
12$82,000$53,455$135,454.70
13$88,000$63,443$151,443.02
14$94,000$74,587$168,587.14
15$100,000$86,971$186,970.62
16$106,000$100,683$206,683.03
17$112,000$115,820$227,820.45
18$118,000$132,486$250,485.91
19$124,000$150,790$274,789.85
20$130,000$170,851$300,850.72

Estimate for planning only, not a projection of any specific investment. It assumes a constant return every period with no fees or taxes, which real markets do not deliver. The return rate is your own input, not a promised or historical figure.

Frequently asked questions

How is compound interest calculated?

Each period your balance earns a return, and that return is added to the balance so the next period earns on a larger amount. This calculator applies your annual rate either monthly or once a year, adds your contribution each period, and repeats for the number of years you set. Growth builds slowly at first and faster later because you are earning returns on your past returns.

Does compounding monthly or annually make a big difference?

Monthly compounding applies one twelfth of the annual rate twelve times a year, so interest starts earning on interest sooner and the ending balance is slightly higher than annual compounding at the same rate. The gap widens with higher rates and longer time frames. You can switch the compounding frequency above to compare the two directly.

What return rate should I use?

That is your own assumption, not a number this tool supplies. A rate is only a planning input, and no real investment returns the same amount every year. Lower, more conservative rates give a more honest floor for planning; you can try a range of rates to see how sensitive the result is to that one assumption.

How much of the final balance is growth versus what I put in?

The tool splits the ending balance into total contributions (your starting balance plus every contribution) and compound growth (everything above that). Over long horizons the growth portion can exceed what you contributed, which is the whole point of compounding. The stat cards and the year-by-year table show both amounts as they build.

Related:Dividend calculatorMortgage calculatorTax calculatorPosition size calculatorReturns backtester