Compound Interest
See exactly how your savings or investments grow when interest compounds over time.
Compounding frequency
How it works
A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)] A = Final amount P = Principal (starting amount) r = Annual interest rate (decimal, e.g. 0.07 for 7%) n = Compounding periods per year (365 / 12 / 4 / 1) t = Time in years PMT = Monthly contribution
Enter your starting amount, annual rate, time period, and an optional monthly contribution. The calculator converts your chosen compounding frequency to an equivalent monthly rate, then steps through each month iteratively — so daily, monthly, quarterly, and annual compounding all produce exact results. The chart and year-by-year table show exactly when your money accelerates.
Why this matters
Compound interest is the single most powerful force in personal finance. A $10,000 investment at 7% p.a. becomes $76,000 after 30 years with no extra contributions — a 7.6× return. Add $200/month and the same scenario produces over $325,000. Starting one year earlier, or increasing your rate by 1%, creates tens of thousands of dollars of difference. This calculator makes that invisible math visible before you commit.
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The complete guide to compound interest
Formulas, examples, and tips explained in plain English