A 4-step walkthrough
Watch the animated demo, then scroll down to try it with your own numbers.
Compound Interest Calculator
A visual compound interest calculator built for clarity. Drag the sliders — see the future, adjusted for inflation, frequency, and reality.
Growth over time
Year-by-year breakdown
// detailed schedule| Year | Start balance | Contributions | Interest earned | End balance |
|---|
Try a real scenario
// click to loadPro tips for compounding
// the fine print most missTime beats timing
Starting 10 years earlier with half the contribution usually beats starting late with double. Years is the most powerful variable.
Rule of 72
To estimate doubling time, divide 72 by your interest rate. At 8% your money doubles every 9 years.
Compare APY, not APR
A 5% APR compounded monthly equals 5.12% APY. Always compare APY-to-APY across products.
Automate contributions
The biggest predictor of hitting a goal is automation. If saving needs a monthly decision, you’ll skip months.
Mind real returns
A 4% return with 3% inflation is just 1% real. Check the inflation-adjusted balance — that’s what you’ll actually feel.
Tax-advantaged first
Roth IRAs, 401(k)s, ISAs, NPS — wrappers let compounding work tax-free. Huge boost over decades.
Frequently asked questions
// the basicsWhat is compound interest?
Compound interest is interest calculated on the initial principal AND on the accumulated interest from previous periods. Each period, you earn interest on a bigger and bigger base — creating exponential rather than linear growth.
What’s the formula behind this calculator?
The future value formula is FV = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]. This calculator solves it numerically year-by-year so you can see the breakdown.
Does compounding frequency matter much?
At low rates, very little. At 5% APR, daily compounding earns about 0.12% more than annual. At higher rates the gap widens, but it’s almost always dwarfed by your contribution rate and time horizon.
Should I trust historical 7–10% returns?
The S&P 500’s long-term real return is about 7% after inflation, but this assumes you stay invested through deep bear markets. Model multiple scenarios — pessimistic, base, optimistic.