How the compound interest calculator works
Compound interest grows your principal because each period's interest is added to the balance, so future interest is earned on interest already accrued.
A = P × (1 + r/n)n × t
Where P is the principal, r is the annual interest rate (as a decimal), n is the number of compounding periods per year, and t is time in years.
Step-by-step guide
- Enter your principal (starting) amount.
- Set the annual interest rate.
- Choose the number of years the money will stay invested.
- Select how often interest compounds — more frequent compounding produces slightly higher returns at the same nominal rate.
Why time matters more than rate
Because compounding is exponential, extending the time period tends to have a larger impact on the final amount than a small increase in rate — this is the core argument for starting to invest early rather than waiting to invest a larger amount later.
Frequently asked questions
It matters, but less than the rate or time period. At 8% for 10 years, monthly compounding versus annual compounding differs by only a few percentage points in the final amount — time in the market matters far more.
A fixed deposit is one real-world application of compound interest, typically compounded quarterly. This calculator works for any compound-interest scenario, not just FDs.
Simple interest is calculated only on the original principal for the whole term. Compound interest is calculated on the principal plus previously earned interest, so it grows faster over time.