Compound Interest Calculator
Model how an initial investment plus regular monthly contributions grows over time, with a year-by-year table and growth chart.
Growth by year
| Year | Contributed | Interest | Balance |
|---|---|---|---|
| 1 | $16,000.00 | $1,054.96 | $17,054.96 |
| 2 | $22,000.00 | $2,695.47 | $24,695.47 |
| 3 | $28,000.00 | $4,970.15 | $32,970.15 |
| 4 | $34,000.00 | $7,931.62 | $41,931.62 |
| 5 | $40,000.00 | $11,636.89 | $51,636.89 |
| 6 | $46,000.00 | $16,147.68 | $62,147.68 |
| 7 | $52,000.00 | $21,530.87 | $73,530.87 |
| 8 | $58,000.00 | $27,858.86 | $85,858.86 |
| 9 | $64,000.00 | $35,210.07 | $99,210.07 |
| 10 | $70,000.00 | $43,669.42 | $113,669.42 |
| 11 | $76,000.00 | $53,328.89 | $129,328.89 |
| 12 | $82,000.00 | $64,288.09 | $146,288.09 |
| 13 | $88,000.00 | $76,654.89 | $164,654.89 |
| 14 | $94,000.00 | $90,546.13 | $184,546.13 |
| 15 | $100,000.00 | $106,088.33 | $206,088.33 |
| 16 | $106,000.00 | $123,418.52 | $229,418.52 |
| 17 | $112,000.00 | $142,685.10 | $254,685.10 |
| 18 | $118,000.00 | $164,048.81 | $282,048.81 |
| 19 | $124,000.00 | $187,683.68 | $311,683.68 |
| 20 | $130,000.00 | $213,778.24 | $343,778.24 |
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How Compound Interest Builds Wealth Over Time
Compound interest means returns are earned on prior returns, not just on the original deposit. The standard formula is A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of compounding periods each year, and t the number of years. Adding a recurring contribution turns it into a future-value-of-an-annuity problem, which is exactly what this calculator solves month by month.
Two variables dominate the outcome: time and consistency. A $500 monthly contribution at 8% grows to roughly $91,000 after ten years but around $296,000 after twenty — the second decade produces far more than double, because the balance itself is doing most of the earning. Delaying the start by five years typically costs more than increasing the contribution ever recovers, which is why early and automatic beats large and late.
Interpret the result honestly. Investment returns are not a straight line, and a long-run average hides years of losses. Inflation reduces purchasing power, so subtract roughly two to three percentage points for a real-terms view, and account for fund fees and taxes on gains, which compound against you exactly as returns compound for you. This tool is for education and planning, not financial advice.
Frequently asked questions
Monthly. Contributions are added at the end of each month and interest is applied at one twelfth of the annual rate, which matches how most savings and investment accounts behave.