Compound Interest Calculator
See how a balance grows when interest earns interest — with optional regular deposits.
Compound interest is interest earned on both the original amount and the interest already added. The future value is A = P(1 + r/n)^(nt), where n is how many times a year it compounds. $5,000 at 6% compounded monthly for 15 years grows to about $12,290 with no deposits — and far more if you add to it regularly. Enter your numbers to see the total.
These results are estimates for informational purposes only and are not financial, tax, or legal advice. Your actual figures from a lender or the IRS may differ. Consult a qualified professional before making decisions.
Future value after 15 years
$41,352.34
What you put in vs. interest earned
Balance by year
| Year | You put in | Interest | Balance |
|---|---|---|---|
| 1 | $6,200 | $342 | $6,542 |
| 2 | $7,400 | $779 | $8,179 |
| 3 | $8,600 | $1,317 | $9,917 |
| 4 | $9,800 | $1,962 | $11,762 |
| 5 | $11,000 | $2,721 | $13,721 |
| 6 | $12,200 | $3,601 | $15,801 |
| 7 | $13,400 | $4,609 | $18,009 |
| 8 | $14,600 | $5,754 | $20,354 |
| 9 | $15,800 | $7,042 | $22,842 |
| 10 | $17,000 | $8,485 | $25,485 |
| 11 | $18,200 | $10,090 | $28,290 |
| 12 | $19,400 | $11,869 | $31,269 |
| 13 | $20,600 | $13,831 | $34,431 |
| 14 | $21,800 | $15,988 | $37,788 |
| 15 | $23,000 | $18,352 | $41,352 |
About the Compound Interest Calculator
Compound interest is what makes money grow faster over time: each period you earn interest not just on your original balance but on all the interest that came before it, so growth accelerates the longer you leave it alone. The formula is A = P(1 + r/n)^(nt), where P is the starting amount, r is the annual rate, n is the number of compounding periods per year, and t is the number of years. Two levers matter most. The first is time — because growth compounds, the last few years add far more than the first few, which is why starting early beats saving more later. The second is frequency: compounding monthly beats annually, and daily beats monthly, though the gap between monthly and daily is small at ordinary rates. Regular deposits change the picture entirely, since each one starts compounding from the day it lands. A useful shortcut is the Rule of 72: divide 72 by the rate to estimate the years it takes to double, so 6% doubles in about twelve years.
Frequently asked questions
What is the compound interest formula?+
A = P(1 + r/n)^(nt). P is the principal, r the annual rate as a decimal, n the compounding periods per year, and t the number of years. The interest earned is A − P.
How is compound interest different from simple interest?+
Simple interest is charged only on the original principal. Compound interest is charged on the principal plus all previously added interest, so the balance grows faster and the gap widens over time.
Does compounding frequency really matter?+
Yes, but with diminishing returns. More frequent compounding earns slightly more — daily beats monthly beats annually — but at everyday rates the difference between monthly and daily is small. The effective annual yield (APY) captures the true effect.
What is the Rule of 72?+
Divide 72 by the annual rate to estimate how many years it takes an amount to double. At 8%, that's about nine years. It's a quick approximation, most accurate for rates in the 6–10% range.