Compound Interest Calculator
Project growth from a starting balance, regular contributions and a rate of return.
Compound growth
| Year | Contributed | Interest | Balance |
|---|---|---|---|
| 1 | $3,600.00 | $840.68 | $14,440.68 |
| 2 | $3,600.00 | $1,161.69 | $19,202.37 |
| 3 | $3,600.00 | $1,505.92 | $24,308.29 |
| 4 | $3,600.00 | $1,875.02 | $29,783.31 |
| 5 | $3,600.00 | $2,270.81 | $35,654.12 |
| 6 | $3,600.00 | $2,695.22 | $41,949.34 |
| 7 | $3,600.00 | $3,150.30 | $48,699.63 |
| 8 | $3,600.00 | $3,638.28 | $55,937.91 |
| 9 | $3,600.00 | $4,161.53 | $63,699.44 |
| 10 | $3,600.00 | $4,722.61 | $72,022.06 |
| 11 | $3,600.00 | $5,324.26 | $80,946.31 |
| 12 | $3,600.00 | $5,969.39 | $90,515.70 |
| 13 | $3,600.00 | $6,661.16 | $100,776.87 |
| 14 | $3,600.00 | $7,402.94 | $111,779.81 |
| 15 | $3,600.00 | $8,198.35 | $123,578.16 |
| 16 | $3,600.00 | $9,051.25 | $136,229.41 |
| 17 | $3,600.00 | $9,965.81 | $149,795.22 |
| 18 | $3,600.00 | $10,946.48 | $164,341.70 |
| 19 | $3,600.00 | $11,998.05 | $179,939.75 |
| 20 | $3,600.00 | $13,125.63 | $196,665.39 |
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Not financial advice. Results are estimates for general information only and are not financial, investment or tax advice. Figures ignore fees, taxes and inflation unless stated. Consult a qualified adviser before making a decision.
How to use the Compound Interest Calculator
- Enter the starting balance and the contribution you add each period.
- Choose the compounding frequency and the annual return.
- Set the number of years and read the future value, total interest and total contributed.
- Look for the crossover year — the point where annual interest first exceeds annual deposits.
A worked example
1,000 start · no contributions · 7% · 30 years
Future value ≈ 7,610 · interest ≈ 6,610
The last ten years of that run add more than the first twenty combined. Growth follows the number of compounding periods, which is why the time input dominates every other one.
Frequently asked questions
What is compound interest?
Interest calculated on the principal plus all previously accumulated interest, so the balance grows exponentially rather than in a straight line.
How much does compounding frequency change the result?
Less than most people expect. At 7% over 30 years, monthly rather than annual compounding adds roughly 3% to the final balance. Rate and time matter far more.
Does this account for inflation and tax?
No. Figures are nominal and before tax. To think in today's money, enter a real rate — your expected return minus expected inflation.
When are contributions applied?
At the end of each compounding period, which is the standard ordinary-annuity convention and the conservative assumption.
About the Compound Interest Calculator
Compound interest earns returns on previous returns. The future value of a lump sum is:
FV = P × (1 + r/n) ^ (n × t)
where P is the principal, r the annual rate, n the compounding periods per year and t the number of years. Regular contributions add an annuity term, calculated here for a deposit made at the end of each period.
Two things dominate the outcome. Time matters more than rate, because the exponent grows faster than the base: 7% over 30 years multiplies your money by 7.6, while 9% over 20 years multiplies it by 5.6. Contributions dominate early and returns dominate late — the year-by-year table shows the crossover point where annual interest first exceeds annual contributions.
Results are nominal. At 3% inflation, money halves in purchasing power roughly every 24 years, so subtract your inflation assumption from the rate to reason in today's money.
Maintained by Ikonode. Last checked against the code on 11 September 2026.
What it does not do
- Contributions are added at the end of each period. A plan that pays at the start earns one extra period of interest and will not match.
- The rate is constant and the figures are nominal, before tax and before inflation. Enter a real rate — return minus inflation — to reason in today’s money.
- It is a projection from your assumptions, not a forecast, and not financial advice.