📈 Compound Interest Calculator
See how your savings or investments grow with compound interest and regular monthly contributions, year by year.
Quick answer: Compound interest formula: A = P(1 + r/n)^(nt). Example: $10,000 at 7% compounded monthly grows to about $40,387 in 20 years without any extra contributions.
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Compound Interest Calculator inputs
Result
Balance after 20 years
$144,572.72
- Total contributions
- $58,000
- Interest earned
- $86,573
- Growth multiple
- 2.49×
- Rule of 72 doubling time
- 10.3 years
| Year | Total contributed | Total interest | Balance |
|---|---|---|---|
| 1 | $12,400.00 | $801.42 | $13,201.42 |
| 2 | $14,800.00 | $1,834.27 | $16,634.27 |
| 3 | $17,200.00 | $3,115.28 | $20,315.28 |
| 4 | $19,600.00 | $4,662.39 | $24,262.39 |
| 5 | $22,000.00 | $6,494.83 | $28,494.83 |
| 6 | $24,400.00 | $8,633.24 | $33,033.24 |
| 7 | $26,800.00 | $11,099.74 | $37,899.74 |
| 8 | $29,200.00 | $13,918.03 | $43,118.03 |
| 9 | $31,600.00 | $17,113.55 | $48,713.55 |
| 10 | $34,000.00 | $20,713.58 | $54,713.58 |
| 11 | $36,400.00 | $24,747.34 | $61,147.34 |
| 12 | $38,800.00 | $29,246.20 | $68,046.20 |
| 13 | $41,200.00 | $34,243.79 | $75,443.79 |
| 14 | $43,600.00 | $39,776.14 | $83,376.14 |
| 15 | $46,000.00 | $45,881.93 | $91,881.93 |
| 16 | $48,400.00 | $52,602.60 | $101,002.60 |
| 17 | $50,800.00 | $59,982.60 | $110,782.60 |
| 18 | $53,200.00 | $68,069.60 | $121,269.60 |
| 19 | $55,600.00 | $76,914.70 | $132,514.70 |
| 20 | $58,000.00 | $86,572.72 | $144,572.72 |
How compound interest grows your money
With compound interest, the interest you earn is added to your balance and then earns interest itself. The effect is small in the first years and dramatic later – notice how the interest portion of the chart overtakes your contributions over time. Starting early matters more than starting big.
A = P(1 + r/n)nt + PMT × [((1 + i)m − 1) ÷ i]
Here P is the initial deposit, r the annual rate, n the compounding frequency and t the number of years; the second term adds monthly contributionsPMT over m months at the equivalent monthly rate i.
Making the most of compounding
- Start now – ten extra years of compounding can double the final balance.
- Contribute regularly, even small amounts, and increase them as your income grows.
- Minimize fees and taxes; a 1% annual fee can consume a large share of long-term growth.
- Reinvest returns instead of withdrawing them.
Returns are illustrative and assume a constant rate. Real investment returns vary and are not guaranteed.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original deposit and on the interest already added. Over long periods this “interest on interest” makes savings grow exponentially.
What is the compound interest formula?
A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of compounding periods per year and t the number of years. Regular contributions are added on top as a growing series.
How often is interest compounded?
Savings accounts often compound daily or monthly, bonds semi-annually and many investment illustrations annually. More frequent compounding gives a slightly higher effective yield.
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% a year, money doubles in roughly 9 years.