Compound Interest Calculator
See what a lump sum grows to over time, and how much of the final figure is interest rather than the money you put in.
—
How it works
Compound interest pays interest on the interest already earned, not just on your original deposit. That is what makes the growth curve bend upwards instead of running in a straight line.
How often interest is added matters. The same annual rate compounded monthly produces slightly more than compounded yearly, because each addition starts earning immediately.
A = P × (1 + r ÷ n)^(n × t)
- A — the future value — what you end up with
- P — the principal — your starting amount
- r — the annual interest rate as a decimal (5% = 0.05)
- n — the number of times interest compounds per year
- t — the term in years
Worked example
1,000 invested at 5% compounded monthly for 10 years
Inputs
Results
Compounded once a year instead of monthly, the same deposit reaches only 1,628.89 — the frequency is worth 18 on this example.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus all interest already added, so growth accelerates over time.
Does compounding frequency make much difference?
Less than most people expect at ordinary rates. In the example above, monthly rather than annual compounding adds about 1% to the ten-year result. It matters far more at high rates or over very long terms.
Can I include regular monthly contributions?
Not in this calculator — it models a single lump sum. Use the SIP calculator for recurring deposits, or the savings goal calculator to work backwards from a target.
Does this account for inflation or tax?
No. The result is a nominal figure. Use the inflation-adjusted return calculator to see what it is worth in today’s money.
More in Savings & Investing
SIP Calculator
Project what investing a fixed amount every month grows to — and see how much of the final figure you contributed versus what the market did.
PersonalStep-up SIP Calculator
Raise your monthly investment a little each year as your income grows, and see how much difference that single habit makes over a full term.
PersonalSWP Withdrawal Calculator
Draw a monthly income from a lump sum and find out how long it lasts — the question that matters most once you stop earning.
PersonalSavings Goal Calculator
Start from the number you need and the date you need it by, and find out what that means every month.
PersonalRetirement Calculator
Two numbers decide a retirement plan: what you will need, and what you are on course to have. This puts them side by side.
PersonalXIRR Calculator
The only honest way to measure a portfolio you have added to and withdrawn from at irregular intervals. Paste your dated cashflows and get the annualised return.