Free Compound Interest Calculator
Project investment or savings growth with regular contributions. Shows total contributed vs interest earned, plus year-by-year breakdown.
Final balance after 30 years
$650,568
$185,000
$465,568
Year-by-year breakdown
| Year | Total contributed | Interest earned | Balance |
|---|---|---|---|
| 1 | $11,000 | $558 | $11,558 |
| 2 | $17,000 | $1,590 | $18,590 |
| 3 | $23,000 | $3,130 | $26,130 |
| 4 | $29,000 | $5,215 | $34,215 |
| 5 | $35,000 | $7,885 | $42,885 |
| 6 | $41,000 | $11,181 | $52,181 |
| 7 | $47,000 | $15,149 | $62,149 |
| 8 | $53,000 | $19,839 | $72,839 |
| 9 | $59,000 | $25,300 | $84,300 |
| 10 | $65,000 | $31,591 | $96,591 |
| 11 | $71,000 | $38,770 | $109,770 |
| 12 | $77,000 | $46,901 | $123,901 |
| 13 | $83,000 | $56,054 | $139,054 |
| 14 | $89,000 | $66,303 | $155,303 |
| 15 | $95,000 | $77,726 | $172,726 |
| 16 | $101,000 | $90,409 | $191,409 |
| 17 | $107,000 | $104,442 | $211,442 |
| 18 | $113,000 | $119,923 | $232,923 |
| 19 | $119,000 | $136,958 | $255,958 |
| 20 | $125,000 | $155,657 | $280,657 |
| 21 | $131,000 | $176,142 | $307,142 |
| 22 | $137,000 | $198,542 | $335,542 |
| 23 | $143,000 | $222,994 | $365,994 |
| 24 | $149,000 | $249,648 | $398,648 |
| 25 | $155,000 | $278,663 | $433,663 |
| 26 | $161,000 | $310,209 | $471,209 |
| 27 | $167,000 | $344,469 | $511,469 |
| 28 | $173,000 | $381,639 | $554,639 |
| 29 | $179,000 | $421,930 | $600,930 |
| 30 | $185,000 | $465,568 | $650,568 |
Quick presets (hypothetical examples only β not guaranteed returns)
π‘ The 7% rate is roughly the long-term US stock market average after inflation. Real returns vary year to year. This calculator assumes a fixed annual rate and constant contributions β useful for planning, not a guarantee.
Common uses
- Plan Your Retirement SavingsSee how monthly contributions grow over decades β the difference between starting at 25 vs 35 is striking.
- Project College Savings (529 Plans)Plan for college tuition by projecting how monthly contributions to a 529 plan grow over 18 years.
- Compare Investing vs Debt PayoffShould you pay off the mortgage early or invest the difference? Run both scenarios.
- Hit a Savings Target by a Specific DateWork backwards: how much do you need to save monthly to hit a savings goal in X years?
- Build Up an Emergency FundCalculate how long it takes to save 3-6 months of expenses in a high-yield savings account.
How It Works
All calculation happens directly in your browser using a hand-written iterative algorithm β no external math library, no server round-trip. Each compounding period is stepped explicitly in JavaScript, so you see results the instant you change any input.
- 1Inputs set the parametersYou supply a starting principal, a monthly contribution, an annual interest rate, a time horizon, and a compounding frequency (daily, monthly, quarterly, or annually). These are validated immediately in the browser β negative rates, non-integer year counts, and rates above 50% are flagged before any calculation runs.
- 2Period-by-period iterationThe core function loops through every compounding period for every year, applying balance = balance Γ (1 + r) + contributionPerPeriod at each step. This step-by-step accumulation is what makes compound interest different from simple interest β earlier periods earn interest on prior interest, and that effect compounds across all subsequent periods.
- 3Optional inflation adjustmentIf you enable inflation adjustment, the tool divides each year's nominal balance by (1 + inflationRate)^year to produce a real (purchasing-power-adjusted) value. This real balance is shown alongside the nominal figure and drawn as a separate dashed line on the growth chart.
- 4Results, chart, and CSV exportThe final balance, total contributed, and total interest are displayed instantly. A year-by-year breakdown table is available below the summary, and you can export it as a CSV file using the browser's Blob API β the file is assembled locally and never sent anywhere. Currency formatting uses the browser's built-in Intl.NumberFormat, so symbols and digit grouping match your locale automatically.
Financial inputs (principal, contributions, rate) are used only in browser memory to run the calculation β nothing is sent to a server.
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