A free simple and compound interest calculator (annual compounding). Educational maths tool.
Simple & Compound Interest Calculator
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| Same inputs, two results — compound pulls ahead over time. |
- Simple interest = (P × R × T) ÷ 100 — flat, on the principal only.
- Compound interest = P × (1 + R/100)^T − P — grows on interest too.
- ₹10,000 at 10% for 3 years → SI ₹3,000, CI ₹3,310.
- The longer the time and higher the rate, the bigger compounding wins.
Simple vs compound interest — the difference
Simple interest is calculated only on the original amount, so it's the same each year:
Simple interest = (P × R × T) ÷ 100
Compound interest adds each period's interest back to the principal, so the base keeps growing:
Compound interest = P × (1 + R/100)^T − P
A worked example
₹10,000 at 10% for 3 years: SI = (10,000 × 10 × 3) ÷ 100 = ₹3,000. CI = 10,000 × (1.10)³ − 10,000 = ₹3,310. The extra ₹310 is interest earning interest — and over 10–20 years that gap becomes huge, which is why compounding is called the "eighth wonder."
Where each one applies
- Compound: fixed deposits, savings, PPF, most investments and most loans.
- Simple: some short-term loans and certain government schemes quote simple interest.
To see compounding at work on a real product, try the FD calculator, the SIP calculator or the PPF calculator. For quick shares and marks, use the percentage calculator.
Frequently asked questions
What's the difference between simple and compound interest?
Simple is on the principal only; compound is on principal plus accrued interest, so it grows faster.
How do I calculate simple interest?
(P × R × T) ÷ 100. ₹10,000 at 10% for 3 years = ₹3,000.
How do I calculate compound interest?
P × (1 + R/100)^T − P. ₹10,000 at 10% for 3 years = ₹3,310.
Why does compound grow faster?
Each period's interest is added to the base and earns interest itself.
About ComplyKraft. Built by Dinesh Kumar S in Chennai — B.Sc. Mathematics, M.Sc. IT. Free calculators and plain-language guides.
Disclaimer: Educational tool. Compound interest here assumes annual compounding; real products may compound more often.