Simple Interest Calculator India 2026 - SI Formula, Examples & Comparison with Compound Interest
TL;DR
Simple Interest (SI) is calculated as P x R x T / 100, where P is principal, R is annual rate, and T is time in years. Unlike compound interest, SI is calculated only on the original principal, not on accumulated interest. In India, simple interest is used in short-term personal loans, some government schemes, and flat-rate car loans. For the same rate and duration, compound interest always yields more than simple interest, which is why understanding the difference matters before taking any loan or making an investment. Key Facts:
- SI Formula: SI = P x R x T / 100
- SI is linear -- double the time, double the interest
- Most Indian bank FDs use compound interest, not simple interest
- Flat-rate personal loans advertise SI but the effective rate is nearly double
- Kisan Vikas Patra and some post office schemes use CI quarterly
- For loan comparison, always convert flat rate to reducing balance rate
Simple Interest Formula & Calculation
The Formula
Simple Interest = (P x R x T) / 100
Total Amount = P + SI = P(1 + RT/100)Where:
P = Principal amount (initial sum)
R = Annual interest rate (%)
T = Time period (in years)
Step-by-Step Example
You deposit Rs 2,00,000 in a scheme offering 8% simple interest for 3 years:
SI = (2,00,000 x 8 x 3) / 100
SI = Rs 48,000
Total Amount = Rs 2,00,000 + Rs 48,000 = Rs 2,48,000
With simple interest, you earn exactly Rs 16,000 per year, every year. The interest does not compound.
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Simple Interest vs Compound Interest: Side-by-Side
Here is how Rs 5,00,000 grows at 8% per annum under both methods:
| Year | SI Total Amount | CI Total Amount (Annual Compounding) | Difference |
|---|---|---|---|
| 1 | Rs 5,40,000 | Rs 5,40,000 | Rs 0 |
| 2 | Rs 5,80,000 | Rs 5,83,200 | Rs 3,200 |
| 3 | Rs 6,20,000 | Rs 6,29,856 | Rs 9,856 |
| 5 | Rs 7,00,000 | Rs 7,34,664 | Rs 34,664 |
| 10 | Rs 9,00,000 | Rs 10,79,462 | Rs 1,79,462 |
| 15 | Rs 11,00,000 | Rs 15,86,084 | Rs 4,86,084 |
| 20 | Rs 13,00,000 | Rs 23,30,478 | Rs 10,30,478 |
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Where Simple Interest Is Used in India
Loans (Flat Rate)
- Personal loans from some NBFCs advertise flat interest rates (which is essentially simple interest on the original principal). A 12% flat rate on a 3-year loan is actually equivalent to ~21% reducing balance rate.
- Car loans from certain dealers quote flat rates. Always ask for the reducing balance (effective) rate.
Government Schemes
- Some older post office schemes historically used simple interest, though most current schemes (PPF, SSY, NSC) use compound interest.
Short-Term Lending
- Informal lending between individuals often uses simple interest.
- Trade credit and short-term business loans may use SI for periods under 1 year.
Flat Rate vs Reducing Balance: The Hidden Cost
| Loan Type | Quoted Rate | Effective Annual Rate | Interest on Rs 10L, 3 years |
|---|---|---|---|
| Flat Rate (SI) | 10% | ~18.5% | Rs 3,00,000 |
| Reducing Balance (CI) | 10% | 10% | Rs 1,61,620 |
| Reducing Balance (CI) | 18.5% | 18.5% | Rs 3,05,412 |
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SI Calculation for Different Time Periods
Sometimes you need to calculate SI for months or days, not full years:
SI (for months) = P x R x (M/12) / 100
SI (for days) = P x R x (D/365) / 100
Quick Reference Table: SI on Rs 1,00,000
| Rate | 3 Months | 6 Months | 1 Year | 2 Years | 5 Years |
|---|---|---|---|---|---|
| 6% | Rs 1,500 | Rs 3,000 | Rs 6,000 | Rs 12,000 | Rs 30,000 |
| 7% | Rs 1,750 | Rs 3,500 | Rs 7,000 | Rs 14,000 | Rs 35,000 |
| 8% | Rs 2,000 | Rs 4,000 | Rs 8,000 | Rs 16,000 | Rs 40,000 |
| 9% | Rs 2,250 | Rs 4,500 | Rs 9,000 | Rs 18,000 | Rs 45,000 |
| 10% | Rs 2,500 | Rs 5,000 | Rs 10,000 | Rs 20,000 | Rs 50,000 |
When to Choose SI vs CI Products
Choose Simple Interest When:
- You need predictable, fixed interest payouts (e.g., retirees wanting steady income)
- The investment period is very short (under 1 year, where the difference is minimal)
- You want to compare loan costs transparently
Choose Compound Interest When:
- You are investing for long-term wealth creation (5+ years)
- You want your returns to accelerate over time
- You are comparing FD rates across banks (all use CI)
Frequently Asked Questions
Q: Do Indian banks use simple interest or compound interest for FDs?
Indian banks use compound interest for Fixed Deposits, typically compounding quarterly. When a bank advertises 7.5% on a 1-year FD, the effective annual yield is slightly higher (about 7.71%) due to quarterly compounding. Only the interest payout option gives you periodic SI-like payments, but the underlying calculation is still compound interest.
Q: How do I convert a flat interest rate to a reducing balance rate?
A rough formula is: Reducing Balance Rate = Flat Rate x 1.8 to 1.95 (depending on tenure). For a more accurate conversion, use the formula: Effective Rate = (2 x n x Flat Rate) / (n + 1), where n is the number of installments. For a 3-year loan (36 EMIs) at 10% flat: Effective Rate = (2 x 36 x 10) / (36 + 1) = 19.46%.
Q: Is simple interest better for short-term borrowing?
For the borrower, simple interest is easier to understand but not necessarily cheaper. What matters is the effective annual rate. A 12% simple interest loan for 6 months costs Rs 6,000 per lakh, while a 12% compound interest loan for 6 months costs Rs 5,830 per lakh (monthly compounding). The difference is small for short periods.
Q: Can I earn simple interest on a savings account in India?
Savings accounts in India calculate interest on a daily balance basis and compound it quarterly. This is compound interest, not simple interest. The daily calculation benefits you when your balance fluctuates. The current savings account rate at major banks is 2.7-3.5%.
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Calculate Simple Interest Instantly
Enter your principal, rate, and time period to calculate SI, total amount, and compare with compound interest. SI Calculator → | Simple Interest Table →