Short answer: Compound interest is interest earned on your interest — and over years, it does most of the growing for you. Enter your starting amount, monthly contribution, annual rate and time below, and this free calculator shows your future value, how much you put in, and how much of the final number is pure interest.
Last updated: 25 October 2026 · Estimate only — not financial advice.
How the math works
- Future value = initial deposit × (1 + r ÷ n)n×t + contributions grown the same way, where r is the annual rate, n is how many times per year interest compounds, and t is years. Each period, interest is calculated on a slightly bigger balance — that is the whole trick.
- Total invested = your initial deposit + every monthly contribution. This is the money that actually came out of your pocket.
- Total interest = future value − total invested. In long runs this number often passes what you put in — that is compounding doing its job.
- Why time beats rate: doubling the years roughly quadruples the effect of compounding, while doubling the rate only doubles it. Starting 10 years earlier usually beats finding a rate 2% higher.
- Contributions are added at the end of each compounding period in this calculator, so a contribution does not earn interest in the same period it is made. Monthly contributions are spread evenly across the compounding period you choose.
Worked example (illustrative — not a real account, not advice)
You start with $10,000, add $200 a month, earn 7% a year compounded monthly, for 20 years:
- Total invested: $10,000 + (240 × $200) = $58,000.00
- Future value: $144,572.72
- Total interest earned: $144,572.72 − $58,000.00 = $86,572.72
More than half the final balance is interest, not money you put in. Cut the time to 10 years instead and the same plan reaches only about $54,700 — the second decade adds roughly $90,000, because compounding accelerates as the balance grows.
FAQ
What is the difference between compound and simple interest?
Simple interest pays only on your original deposit, every year the same amount. Compound interest pays on the deposit plus all interest earned so far, so each year's interest is bigger than the last. Over 20 years at 7%, $10,000 grows to $24,000 with simple interest but to about $38,700 compounded yearly.
Is APY the same as the interest rate I enter here?
Not quite. APY (annual percentage yield) already includes the effect of compounding, while APR usually does not. If your bank quotes an APY, use that as the rate with monthly compounding for a close match — our APY vs APR guide explains the difference in full.
Does this calculator include taxes or fees?
No — it shows growth before tax, fees and inflation. Real returns are lower: in most countries interest and crypto-staking rewards are taxable income, and inflation quietly eats 2–3% a year. Treat the result as the optimistic ceiling, not the number you will actually keep.
Can I lose money with compound interest?
Compound interest itself only grows a balance, but the rate is never guaranteed — savings rates change, investments fall, and crypto yields can vanish. A calculator assumes one fixed rate for the whole period; real life does not. Never plan your finances on a single assumed rate.
Related from Bia Crypto
- Crypto Staking Rewards Calculator 2026 — staking rewards compound too; see what your yield really adds up to.
- APY vs APR Explained — the rate definitions this calculator depends on.
- Crypto Profit Calculator — work out profit and ROI on a single trade.
- Is Binance Safe and Legit in 2026? — today's guide: fees, regulation and red flags checked before you park money anywhere.
Sources
Disclaimer: This tool gives a simplified estimate for education only. It is not financial advice. Rates are not guaranteed, and actual returns depend on taxes, fees, inflation and market risk.
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