Finance
Compound Interest Calculator
See how your money grows year by year — with monthly contributions and a visual schedule.
Result
Final balance
$694,709
Total contributions
$190,000
Total interest earned
$504,709
Growth over time
Year-by-year schedule
| Year | Start | Contributions | Interest | End balance |
|---|---|---|---|---|
| 1 | $10,000 | $6,000 | $955 | $16,955 |
| 2 | $16,955 | $6,000 | $1,458 | $24,413 |
| 3 | $24,413 | $6,000 | $1,997 | $32,411 |
| 4 | $32,411 | $6,000 | $2,575 | $40,986 |
| 5 | $40,986 | $6,000 | $3,195 | $50,182 |
| 6 | $50,182 | $6,000 | $3,860 | $60,042 |
| 7 | $60,042 | $6,000 | $4,573 | $70,614 |
| 8 | $70,614 | $6,000 | $5,337 | $81,952 |
| 9 | $81,952 | $6,000 | $6,157 | $94,108 |
| 10 | $94,108 | $6,000 | $7,036 | $107,144 |
| 11 | $107,144 | $6,000 | $7,978 | $121,122 |
| 12 | $121,122 | $6,000 | $8,988 | $136,110 |
| 13 | $136,110 | $6,000 | $10,072 | $152,182 |
| 14 | $152,182 | $6,000 | $11,234 | $169,416 |
| 15 | $169,416 | $6,000 | $12,480 | $187,895 |
| 16 | $187,895 | $6,000 | $13,815 | $207,710 |
| 17 | $207,710 | $6,000 | $15,248 | $228,958 |
| 18 | $228,958 | $6,000 | $16,784 | $251,742 |
| 19 | $251,742 | $6,000 | $18,431 | $276,173 |
| 20 | $276,173 | $6,000 | $20,197 | $302,370 |
| 21 | $302,370 | $6,000 | $22,091 | $330,461 |
| 22 | $330,461 | $6,000 | $24,121 | $360,582 |
| 23 | $360,582 | $6,000 | $26,299 | $392,881 |
| 24 | $392,881 | $6,000 | $28,634 | $427,515 |
| 25 | $427,515 | $6,000 | $31,138 | $464,653 |
| 26 | $464,653 | $6,000 | $33,822 | $504,475 |
| 27 | $504,475 | $6,000 | $36,701 | $547,176 |
| 28 | $547,176 | $6,000 | $39,788 | $592,964 |
| 29 | $592,964 | $6,000 | $43,098 | $642,062 |
| 30 | $642,062 | $6,000 | $46,647 | $694,709 |
How compound interest works
Compound interest means your interest earns interest. Each year, the previous year's interest is added to your principal, so the next year's interest is calculated on a larger balance. Over decades, this produces dramatic exponential growth.
Add monthly contributions and the effect compounds further. A modest $500/month at 7% for 30 years grows to over $600,000 — even though you only contributed $180,000. Time is the most powerful lever, by far.
Frequently Asked Questions
What is compound interest?▾
Compound interest is interest earned on both your original deposit and on previously earned interest. Over long periods, this "interest on interest" effect produces exponential growth — the engine behind retirement savings.
What is the formula for compound interest?▾
A = P(1 + r/n)^(nt). A is the final amount, P is the principal, r is the annual rate (decimal), n is compounding periods per year, t is the number of years. With monthly contributions, the math is more complex but the same principle applies.
How often should interest compound?▾
More frequent compounding = slightly more growth, but the difference is tiny over normal rates. At 7% over 30 years, $10,000 grows to ~$76,123 (annual) vs ~$81,648 (daily) — about 7% more. The biggest lever is the rate and time, not the frequency.
What is a realistic interest rate?▾
For US stock market index funds, the long-term real return (after inflation) has been about 6–7% per year. High-yield savings accounts pay 4–5%; bonds 3–5%; CDs 4–5%. Always model conservatively (5–7%) to avoid disappointment.
How long until my money doubles?▾
Use the Rule of 72: years to double ≈ 72 / annual rate. At 6% your money doubles in ~12 years; at 8% in ~9 years; at 10% in ~7.2 years. It is a great mental shortcut for evaluating opportunities.