Simple Interest Calculator
A simple interest calculator is a free online tool that computes the interest on a loan or investment when interest is calculated only on the original principal — never on accumulated interest.
Simple vs Compound Interest
Simple interest is calculated only on the principal, never on accumulated interest.
How to use Simple Interest Calculator
- Enter principal — Type the loan or investment amount.
- Set interest rate — Enter the annual interest rate.
- Choose duration — Enter the period in months or years.
- See total — View interest and total amount.
Key features
- Instant SI calculation
- Formula display
- Monthly and yearly interest breakdown
- Total amount calculation
- Works for loans and investments
- Comparison with compound interest
What is Simple Interest?
Simple interest is the most straightforward way to calculate the cost of borrowing or the return on investment. It's computed only on the original principal amount — never on accumulated interest. If you borrow ₹1 lakh at 10% simple interest for 5 years, you pay ₹10,000 per year, totaling ₹50,000 interest. The principal never changes for interest calculation.
The Simple Interest Formula
SI = (P × R × T) / 100. Where P is principal, R is annual rate (%), and T is time in years. Total amount = P + SI. For monthly calculations: SI = (P × R × T) / (100 × 12) with T in months. This formula has been used for centuries because it's fair, transparent, and predictable.
Simple vs Compound Interest
Simple interest pays the same amount every year. Compound interest grows every year because you earn interest on your interest. Example: ₹1 lakh at 10% for 10 years: Simple = ₹2 lakh total. Compound (yearly) = ₹2.59 lakh. Over 30 years: Simple = ₹4 lakh. Compound = ₹17.45 lakh. The difference is enormous — which is why compounding is the foundation of wealth building.
Where Simple Interest is Used
Car loans from some traditional banks, short-term personal loans, interest on delayed tax payments, some post office schemes, informal lending between individuals, and certain corporate bonds. If you want predictable payments without compounding complexity, SI-based instruments are ideal. For long-term investments, always prefer compound interest.
Pro tips
- Simple interest is better for borrowers, worse for investors long-term
- Use SI for short-term loans to avoid compounding
- Formula: SI = (P × R × T) / 100
- For monthly SI, use T in months and divide by 1200
Common use cases
- Short-term loan calculations
- Simple interest on deposits
- Interest on delayed payments
- Educational loan understanding
- Quick investment projections
Frequently asked questions
What is simple interest?+
Simple interest is calculated only on the original principal, never on accumulated interest. Formula: SI = (P × R × T) / 100.
When is simple interest used?+
In short-term loans, car loans in some banks, interest on delayed payments, and certain government schemes.
Is simple interest lower than compound interest?+
Yes — always. Over time, the gap widens dramatically.
How do I calculate monthly SI?+
Divide the annual rate by 12 and use months as time. Or divide annual SI by 12.
Is SI used for home loans?+
No — home loans use reducing balance (a form of compound interest). SI is mostly for short-term or informal loans.
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