Simple Interest Calculator
Calculate simple interest on your savings, loans, or investments instantly
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= (₹1,00,000 × 8% × 5) / 100 = ₹40,000
📖 Complete Guide to Simple Interest
Simple Interest is the most basic form of interest calculation — interest is charged only on the original principal amount. While most modern financial products use compound interest, understanding simple interest is fundamental for comparing loan offers, quick mental calculations, and short-term financial planning.
📐 Simple Interest Formula
SI = P × R × T / 100
Total Amount = Principal + SI = P × (1 + R×T/100)
📊 SI vs CI — Growth Comparison
| ₹1 Lakh at 10% | Simple Interest | Compound Interest | Difference |
|---|---|---|---|
| 1 Year | ₹10,000 | ₹10,000 | ₹0 |
| 3 Years | ₹30,000 | ₹33,100 | ₹3,100 |
| 5 Years | ₹50,000 | ₹61,051 | ₹11,051 |
| 10 Years | ₹1,00,000 | ₹1,59,374 | ₹59,374 |
| 20 Years | ₹2,00,000 | ₹5,72,750 | ₹3,72,750 |
🏦 Where Simple Interest is Used
- Car loan flat rates: Some dealers quote SI-based flat rates (always convert to reducing rate for true comparison)
- Non-cumulative FD payouts: Monthly/quarterly interest payouts from FDs are effectively SI
- Short-term loans: Personal loans under 1 year sometimes use simple interest
- Quick estimation: SI is perfect for mental math — ₹1 Lakh at 10% = ₹10,000/year
💡 Key Takeaways
- For investing: Always choose compound interest products (FDs, mutual funds, PPF)
- For borrowing: Ask if the rate is flat (SI) or reducing (CI) — flat rates cost more
- For short periods (under 1 year): SI and CI give nearly identical results
- For long-term wealth: SIP in mutual funds uses the power of compounding for maximum growth
❓ Frequently Asked Questions
Q: What is Simple Interest?
A: Simple Interest (SI) is interest calculated only on the original principal amount. Unlike compound interest, SI does not earn interest on previously earned interest. Formula: SI = P × R × T / 100, where P = Principal, R = Annual Rate (%), T = Time in years.
Q: What is the Simple Interest formula?
A: SI = P × R × T / 100. Total Amount = P + SI = P × (1 + R×T/100). For example: ₹1,00,000 at 8% for 3 years → SI = 1,00,000 × 8 × 3 / 100 = ₹24,000. Total amount = ₹1,24,000.
Q: Simple Interest vs Compound Interest — what's the difference?
A: SI calculates interest only on original principal. CI calculates interest on principal + accumulated interest. For ₹1 Lakh at 10% for 10 years: SI = ₹1 Lakh (total ₹2L), CI = ₹1.59 Lakh (total ₹2.59L). CI gives ₹59,374 more over 10 years.
Q: Where is Simple Interest used in real life?
A: SI is used in: Short-term personal loans, car loans from some dealers (flat rate), simple savings calculations, treasury bills, some agricultural loans, informal lending, and short-term fixed deposits. Most modern banking uses compound interest.
Q: How to convert flat rate to reducing rate?
A: Flat rate (simple interest) on loans is roughly 1.8-2x the equivalent reducing rate. A 10% flat rate ≈ 18-20% reducing balance rate. Always ask your lender to clarify which rate they're quoting — reducing balance rate is the true cost of borrowing.
Q: What is the difference between flat rate and reducing rate?
A: Flat rate: Interest calculated on full original principal throughout the loan. Reducing rate: Interest calculated on remaining outstanding principal. For a ₹1 Lakh loan: 10% flat rate costs more than 10% reducing rate because you pay interest on the full amount even as you repay principal.
Q: Is Simple Interest ever better than Compound Interest?
A: For borrowers: SI (flat rate) often appears lower but costs more — always compare effective rates. For investors: CI is always better as your returns earn returns. SI is simpler to understand and calculate, making it useful for quick mental math and short-term estimates.
Q: How to calculate monthly Simple Interest?
A: Monthly SI = P × R / (12 × 100). For ₹5 Lakh at 6% annual rate: Monthly interest = 5,00,000 × 6 / (12 × 100) = ₹2,500 per month. This is how non-cumulative FDs calculate monthly interest payouts.
Q: What is the SI on ₹1 Lakh for 1 year at 7%?
A: SI = 1,00,000 × 7 × 1 / 100 = ₹7,000. Monthly: ₹583. The total amount after 1 year = ₹1,07,000. Compare with compound interest at 7% quarterly: ₹1,07,186 — difference of just ₹186 for 1 year.
Q: Can I use SI for FD calculation?
A: Banks use compound interest (quarterly) for FDs, not simple interest. However, non-cumulative FDs that pay interest monthly/quarterly effectively use simple interest since interest is paid out, not reinvested. For accurate FD calculation, use our FD Calculator.
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