Compound Interest Calculator
See how a lump-sum investment grows over time with compound interest, and how much of the final value is interest.
This calculator provides an estimate based on a fixed rate you enter; real investment returns vary. See our Disclaimer.
The formula
A = P × (1 + r/n)ⁿᵗ, where P is the initial amount, r is the annual rate (as a decimal), n is the number of times interest compounds per year, and t is the number of years.
Worked example
100,000 invested at 8% annual interest, compounded annually, for 5 years grows to 100,000 × 1.08⁵ ≈ 146,932.81 — meaning about 46,932.81 comes from compounding rather than the original deposit.
Why compounding frequency matters
The more often interest compounds within a year, the faster the balance grows, because each compounding period's interest starts earning its own interest sooner. The difference is modest at low rates but becomes noticeable over long periods or at higher rates.
The same deposit at four frequencies
A deposit of 5,000 at 5% for 20 years ends at 13,266.49 with annual compounding, 13,425.32 semi-annually, 13,507.42 quarterly and 13,563.20 monthly. Monthly compounding adds 296.71 over annual, and each step to a higher frequency adds less than the one before it.
A quick check with the Rule of 72
Dividing 72 by the annual rate estimates the years needed to double. At 8% that is 72 ÷ 8 = 9 years, and the calculator agrees: 1,000 at 8% compounded annually for 9 years becomes 1,999.00, just under double.
What this calculator leaves out
- Regular deposits or withdrawals. For a monthly saving habit, use the compound interest calculator with monthly contributions.
- Tax on the interest and any account fees, which lower what you actually keep.
- Changes in the rate. The result assumes one fixed rate for the whole period.
- Inflation, which reduces what the final amount can buy. The Inflation Calculator shows that effect.
Examples, and what changes the result
10,000 at 7% a year for 10 years becomes 19,671.51 with annual compounding, an interest of 9,671.51. The same rate compounded monthly gives 20,096.61, which is 425.10 more, so the compounding frequency matters even though the rate is the same. At a rate of 0% the final amount is just the 10,000 you started with.
The calculator offers annual, semi-annual, quarterly and monthly compounding. A negative number of years returns "Please enter positive values." It models one lump sum with no further deposits, so use the contributions version of this calculator when you add money regularly.
Guides
- Compound vs Simple Interest and the Rule of 72 — How simple and compound interest differ, why compounding frequency and the effective rate matter, and how far the Rule of 72 can be trusted.
- Compounding Frequency Compared: Annual to Daily — Worked examples of how much the compounding frequency changes a balance, why the gain flattens out, and when it matters more than it looks.
- FD vs RD vs PPF: How Each Compounds — How each of the three compounds and gets its rate, and what the calculators simplify. A comparison of mechanics, not a ranking.
Frequently asked questions
What's the difference between compound and simple interest?
Simple interest is calculated only on the original principal every period. Compound interest is calculated on the principal plus any interest already earned, so the growth accelerates over time.
Does this account for taxes or fees?
No. This is a pure mathematical projection of growth at your stated rate — real accounts may involve taxes, account fees, or a return rate that changes year to year.