EMI Calculation Formula Explained

Reducing balance EMI formula explained — amortisation schedule example, flat vs reducing rate comparison, Excel formula.

📅 Updated 2026-03-14 🕒 5 min read 📋 Free Calculator Included

📚 EMI Formula Deep Dive

The EMI formula is rooted in the time value of money — a rupee today is worth more than a rupee tomorrow. The reducing balance method ensures you pay interest only on outstanding principal at each point, making it fairer than flat-rate methods.

Standard EMI FormulaEMI = [P × r × (1+r)^n] / [(1+r)^n − 1]

Per ₹1 Lakh Rule (8.5%, 20 yr)EMI ≈ ₹868 per ₹1 lakh borrowed

📋 How Each EMI Is Split (Amortisation)

🌟 ₹30L, 8.5%, 20 yrs — EMI ₹26,082

Month 1: Interest ₹21,250 (82%) | Principal ₹4,832 (18%)

Month 60 (Yr 5): Interest ₹19,604 (75%) | Principal ₹6,478 (25%)

Month 120 (Yr 10): Interest ₹17,326 (66%) | Principal ₹8,756 (34%)

Month 200 (Yr 17): Interest ₹10,283 (39%) | Principal ₹15,799 (61%)

Month 240 (final): Interest ₹183 (<1%) | Principal ₹25,899 (99%)

Why Prepaying Early Saves More

The outstanding principal is highest in early years, so every rupee prepaid in Years 1–5 saves 4–5x the interest it would save in Years 15–20. Annual bonus prepayment early in the loan lifecycle is mathematically optimal.

📝 Flat Rate vs Reducing Balance

Flat Rate EMI (used by some NBFCs)EMI = (P + P × Rate × Tenure) / (Tenure × 12)
⚠ Effective rate ≈ 1.8–2× the stated flat rate

Method	Stated Rate	Effective Rate	₹5L, 3yr Interest
Flat Rate	12%	~21.5%	₹1,80,000
Reducing Balance	12%	12%	₹96,743
Difference	Same stated!	9.5% more	₹83,257 extra

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❓ Frequently Asked Questions

Do all banks use reducing balance?

Yes — all RBI-regulated banks use reducing balance for retail loans. Some NBFCs may use flat rate — always ask for the reducing balance APR before signing any loan agreement.

How does tenure affect total interest?

₹30L at 8.5%: 10yr = ₹14.6L interest; 20yr = ₹32.5L; 30yr = ₹53.1L. Longer tenure dramatically increases total cost — choose the shortest tenure your cash flow can sustain.

How to calculate EMI in Excel?

=PMT(rate/12, tenure_months, -principal). E.g. =PMT(8.5%/12, 240, -3000000) gives ₹26,082. Note: PMT returns negative in Excel — use =−PMT(...) or wrap in ABS().

🔗 Related Calculators

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💡 Tip: Rule of thumb: ₹1 lakh at 8.5% for 20 yrs = ₹868/month EMI. Scale linearly for any loan amount.