Savings

Compound Interest Calculator

Every year shown, formula visible. See exactly what drives the growth — not just the final number.

Final balance

after 0 years

Principal: $0 · Interest earned: $0

Your investment

Starting amount

Monthly contribution

Annual interest rate (%)S&P 500 historical avg ≈ 10% nominal, 7% inflation-adjusted. HYSA ≈ 4-5%. CD ≈ 4-5%.

Time horizon (years)

Compounding frequency

The formula A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]

Year-by-year breakdown

Year	Balance	Interest earned (year)	Total contributed	Total interest

What this doesn't model: inflation (real purchasing power), taxes on gains (taxable accounts owe capital gains/income tax), or investment fees (even 0.5% annual fees compound significantly over 30 years). For retirement accounts, gains are tax-deferred or tax-free.

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