Compound interest calculator
Updated Updated for 2026 tax law
See how your savings grow when interest earns interest. Add an initial deposit and monthly contributions, pick how often interest compounds, and switch to today's dollars to see the effect of inflation.
- Total contributions (incl. initial)
- $58,000
- Total interest earned
- $86,573
- Interest share of the final balance
- 59.9%
- Effective annual yield (APY)
- 7.229%
- Years to double (exact · rule of 72)
- 9.9 · 10.3
Monthly deposits earn the monthly rate equivalent to monthly (12/yr) compounding, so every dollar earns the same 7.23% APY. Taxes and fees are not included.
Year-by-year table
| Year | Contributions | Interest | Balance | Today's dollars |
|---|---|---|---|---|
| 1 | $12,400 | $801 | $13,201 | $12,817 |
| 2 | $14,800 | $1,834 | $16,634 | $15,679 |
| 3 | $17,200 | $3,115 | $20,315 | $18,591 |
| 4 | $19,600 | $4,662 | $24,262 | $21,557 |
| 5 | $22,000 | $6,495 | $28,495 | $24,580 |
| 6 | $24,400 | $8,633 | $33,033 | $27,665 |
| 7 | $26,800 | $11,100 | $37,900 | $30,816 |
| 8 | $29,200 | $13,918 | $43,118 | $34,038 |
| 9 | $31,600 | $17,114 | $48,714 | $37,335 |
| 10 | $34,000 | $20,714 | $54,714 | $40,712 |
| 11 | $36,400 | $24,747 | $61,147 | $44,174 |
| 12 | $38,800 | $29,246 | $68,046 | $47,726 |
| 13 | $41,200 | $34,244 | $75,444 | $51,374 |
| 14 | $43,600 | $39,776 | $83,376 | $55,121 |
| 15 | $46,000 | $45,882 | $91,882 | $58,976 |
| 16 | $48,400 | $52,603 | $101,003 | $62,941 |
| 17 | $50,800 | $59,983 | $110,783 | $67,025 |
| 18 | $53,200 | $68,070 | $121,270 | $71,233 |
| 19 | $55,600 | $76,915 | $132,515 | $75,571 |
| 20 | $58,000 | $86,573 | $144,573 | $80,046 |
How to use the compound interest calculator
- Enter your starting amount and how much you'll add each month.
- Enter the annual interest rate (APR) and the number of years.
- Choose the compounding frequency from your bank or account terms — savings accounts usually compound daily or monthly.
- Optionally raise your contributions each year, and switch to "today's dollars" to adjust for inflation.
- Hover over the chart or open the year-by-year table; copy the table as CSV for a spreadsheet.
Compound interest formula
Monthly rate i = (1 + r/n)n/12 − 1
Contributions FV = C × ((1 + i)12t − 1) ÷ i (× (1 + i) if deposited at the start of the month)
APY = (1 + r/n)n − 1 · Today's dollars = A ÷ (1 + inflation)t
P = initial deposit, r = annual rate (decimal), n = compounding periods per year, t = years, C = monthly contribution. Example: $10,000 plus $200 a month at 7% compounded monthly for 20 years grows to $144,573. You put in $58,000; $86,573 is interest. In today's dollars at 3% inflation, that's $80,046.
Compounding frequency compared
| Compounding | APY | Balance |
|---|---|---|
| Annually | 5% | $16,288.95 |
| Semiannually | 5.062% | $16,386.16 |
| Quarterly | 5.095% | $16,436.19 |
| Monthly | 5.116% | $16,470.09 |
| Daily | 5.127% | $16,486.65 |
| Continuously | 5.127% | $16,487.21 |
How much $10,000 grows
| Rate | 5 years | 10 years | 20 years | 30 years |
|---|---|---|---|---|
| 3% | $11,616 | $13,494 | $18,208 | $24,568 |
| 5% | $12,834 | $16,470 | $27,126 | $44,677 |
| 7% | $14,176 | $20,097 | $40,387 | $81,165 |
| 10% | $16,453 | $27,070 | $73,281 | $198,374 |
Monthly contributions over time
| Monthly deposit | 10 years | 20 years | 30 years |
|---|---|---|---|
| $100 | $17,308 | $52,093 | $121,997 |
| $250 | $43,271 | $130,232 | $304,993 |
| $500 | $86,542 | $260,463 | $609,985 |
| $1,000 | $173,085 | $520,927 | $1,219,971 |
Disclaimer: Estimates for information only — not tax, legal or financial advice. Investment returns vary and are not guaranteed; taxes and fees are not included.
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Frequently asked questions
What is the compound interest formula?
A = P(1 + r/n)^(nt), where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years. With regular monthly deposits C, add C × ((1 + i)^m − 1) / i, where i is the monthly rate and m the number of months.
How much will $10,000 grow in 10 years?
At 5% compounded monthly, $10,000 becomes $16,470.09. At 7% it becomes $20,096.61.
Does compounding frequency matter much?
Less than people think. $10,000 at 5% for 10 years is $16,288.95 compounded annually and $16,486.65 compounded daily. The rate and the time invested matter far more.
What is the rule of 72?
Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8%, money doubles in about 9 years. It is most accurate for rates between about 6% and 10%.
What does inflation-adjusted mean?
It converts the future balance into today's purchasing power by dividing by (1 + inflation)^years. At 3% inflation, $100,000 in 20 years buys what about $55,368 buys today.
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Estimates for information only — not tax, legal or financial advice.