Introduction
Simple interest grows linearly with time — interest is calculated only on the original principal, not on accumulated interest. It appears in short-term loans, some certificates of deposit, and introductory finance coursework throughout India.
Use our calculator for SI = P × R × T / 100 with instant amount and interest breakdown. Compare with Compound Interest when interest compounds periodically.
Simple Interest Formula
SI = (P × R × T) / 100, where P = principal (₹), R = annual rate (%), T = time in years. Total Amount = P + SI. For months: convert T = months/12.
Step-by-Step Examples
Example: ₹50,000 at 8% for 3 years
SI = (50000 × 8 × 3) / 100 = ₹12,000. Amount = ₹62,000.
Example: 6 months at 10%
T = 0.5 years. SI = (100000 × 10 × 0.5) / 100 = ₹5,000.
Real-Life Applications
- School and college mathematics word problems
- Short-term lending and pawn scenarios
- Quick interest estimates for small loans
- Baseline comparison before compound interest analysis
- Banking and SSC exam preparation
Advantages of Using This Simple Interest
- Clear formula display with substituted values
- Accepts tenure in years or months
- Indian currency formatting
- Side-by-side principal, interest, and total
- Links to compound interest for contrast learning
Common Mistakes to Avoid
- Using months as T without dividing by 12
- Applying simple interest when compounding applies
- Mixing rate per annum with rate per month
- Forgetting to add principal to interest for total amount
- Percent vs decimal rate confusion (8 vs 0.08)
Learn More
What is Simple Interest?
Simple interest is the most straightforward method of calculating interest on a loan or investment. Interest is computed only on the original principal amount throughout the entire period; it does not compound. This makes it easy to calculate and understand, which is why it is commonly taught in school mathematics and used for short-term financial products.
Simple Interest Formula
SI = P × R × T / 100
- P = Principal amount (initial sum)
- R = Rate of interest per annum (%)
- T = Time period in years
Total Amount = P + SI
Worked Example
Principal = ₹50,000, Rate = 8% p.a., Time = 3 years
SI = 50,000 × 8 × 3 / 100 = ₹12,000
Total = ₹50,000 + ₹12,000 = ₹62,000
Simple vs Compound Interest
With simple interest, each year's interest is the same. With compound interest, interest earns interest, growing faster over time. For the same principal, rate, and time, compound interest always yields more (or equal for 1 year).
Real-World Applications
- Short-term personal loans
- Treasury bills and some government bonds
- Bank overdraft facilities
- School and competitive exam problems