Simple & Compound Interest Calculator
Compare simple interest and compound interest side by side, with formulas.
Maths • Banking • Class 8–12Interest shows up everywhere: in school maths, in your savings account, in loans and in fixed deposits. The two basic types are simple interest and compound interest, and the difference between them grows bigger the longer the money stays invested or borrowed.
This calculator shows both side by side, so students can check their answers and anyone can see how much difference compounding makes.
How to use the interest calculator
- Enter the principal (the starting amount).
- Enter the yearly interest rate.
- Enter the time in years.
- Choose how often interest is compounded (yearly, half-yearly, quarterly or monthly).
- Tap Calculate to see simple interest, compound interest and the final amounts.
Formulas
- Simple interest: SI = P × R × T ÷ 100
- Compound amount: A = P × (1 + R ÷ (100 × n))n × T
- Compound interest: CI = A − P
- P = principal, R = yearly rate in %, T = time in years, n = compounding periods per year
A worked example
Take ₹10,000 at 10% a year for 3 years. Simple interest = 10,000 × 10 × 3 ÷ 100 = ₹3,000. With yearly compounding, the amount becomes 10,000 × 1.1 × 1.1 × 1.1 = ₹13,310, so compound interest is about ₹3,310. The extra ₹310 is interest earned on interest.
Where you will use this
- Class 8 to Class 12 maths and competitive exams like SSC and banking.
- Checking FD returns (see our FD calculator).
- Understanding why loan interest adds up (see our EMI calculator).
Frequently asked questions
What is the main difference between SI and CI?
Simple interest is charged only on the original amount. Compound interest is also charged on the interest already added, so it grows faster.
Which one do banks use?
Savings accounts, FDs and most loans use compound interest. Some short-term loans use simple interest.
Can I use this for homework?
Yes. It uses the same formulas as NCERT textbooks, so you can check your answers. Do try the steps yourself first!
Is it free?
Yes, and it needs no sign-up.
