Finance & Money
Compound Interest Calculator
See how an initial amount plus regular contributions grows over time.
How often interest is added to the balance.
Final amount
31,998.32
After 10 years
Your investment grows to about 31,998.32. You put in 22,000.00 and 9,998.32 of that comes from interest - about 31% of the final balance.
Initial investment
10,000.00
Total contributions
12,000.00
Interest earned
9,998.32
Total paid in
22,000.00
Your money vs growth
- Initial investment10,000.0031.3%
- Contributions12,000.0037.5%
- Interest earned9,998.3231.2%
Balance over time
Free to use. No sign-up required.
How it works
Compound interest means interest is added to the balance and then earns interest itself. The more often that happens, the faster the balance grows, which is why the compounding frequency matters.
The calculator steps through every compounding period, applies the periodic rate, then adds any contributions due in that period. Contributions are added at the end of the period, which is the conservative convention.
The result separates what you put in from what the interest produced. Over long periods the interest portion usually overtakes the contributions, and the visual on this page shows when that happens.
Assumptions: the rate is constant for the whole period, contributions never change, and nothing is withdrawn. No tax, inflation, platform fees or investment losses are modelled. A real return is rarely a straight line.
Formula
Compound interest on a lump sum
A = P × (1 + r ÷ n)^(n × t)
P = principal, r = annual rate as a decimal, n = compounds per year, t = years.
Future value of regular contributions
FV = PMT × (((1 + i)^m − 1) ÷ i)
PMT = contribution per period, i = periodic rate, m = number of periods.
Interest earned
final amount − principal − total contributions
Worked examples
1,000 at 5% for 10 years, compounded annually → 1,628.89
The interest earned is 628.89 on an unchanged 1,000 deposit.
The same at monthly compounding → 1,647.01
Compounding twelve times a year instead of once adds about 18 over the decade.
100 a month for 10 years at 5%, compounded monthly → 15,528.23
You contribute 12,000 and the interest adds 3,528.23 on top.
Frequently asked questions
What does compounding frequency actually change?
How often interest is added to the balance. More frequent compounding means interest starts earning interest sooner, so the final figure is slightly higher for the same headline rate. The effect is real but usually small compared with the rate itself.
When are contributions added?
At the end of each period. If you contribute more often than the balance compounds, the contributions for that period are added together at the end of it. This slightly understates growth rather than overstating it.
Does this account for tax or inflation?
No. The figures are before tax and in nominal terms. Tax treatment of savings and investments differs by country, and inflation reduces what the final amount will actually buy.
Is this a projection of investment returns?
No. It shows what a constant rate would produce. Real investment returns vary year to year and can be negative. Use it to understand how compounding works, not to predict an outcome.