Mathematical Framework & SimulatorCategory: Extra EMI, Principal & Payoff Guides →

How is Prepayment Interest Calculated?

Understand the exact daily reducing balance mathematics behind loan prepayments and simulate how reducing principal saves thousands in compound interest.

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🏡 Mortgage Payoff (Extra Payments)⚡ Loan Payoff (Extra Payments)⏱️ Payoff Time Calculator 🎯 Extra EMI Prepayment 🏡 Home Loan Extra EMI 💰 Home Loan Extra Payment 💵 Extra Principal Payments 💡 What is Extra Principal?📐 Calculate Extra Principal 🚀 Effect of Extra Principal 🧮 Prepayment Interest Formula ⚖️ Prepayment Penalty Calculator 📑 Prepaid Expenses Calculator 📊 Universal Loan Extra Payments 📅 Mortgage Extra Monthly ⚡ Mortgage Prepayment (Extra)🏦 Prepayment Mortgage Suite 📖 Prepayment Amount Meaning

📐 The Fundamental Prepayment Mathematics

In an amortizing loan (such as home mortgages, auto loans, or personal loans), interest is not a fixed flat fee. It is calculated dynamically based on the current outstanding balance.

1. Daily Interest Accrual Formula

Interestday = (P × r) / 365

Where P = current principal, r = annual interest rate as a decimal.

2. Post-Prepayment Effect

New Principal = Poriginal - Extra Payment

Immediate drop in P lowers all future interest accrued every single day thereafter.

Interactive Interest Simulator

Loan Principal (P)$

Annual Rate (r)% p.a.

Tenure (Years)20 Yrs

Yrs

Prepayment Injection Details

One-Time Prepayment AmountLump Sum

Prepayment Made in Month #Timeline

Month

Additional Extra Monthly Payment+ Monthly

Net Interest Eliminated by Calculation

Interest cost reduced from original schedule!

Daily Interest (Before)

$0 / day

On Initial Principal

Daily Interest (After Prepay)

$0 / day

-$0 / day savings

Original Total Interest

Over full term

New Total Interest

Saved 0%

📊 Exact Step-by-Step Calculation:

Scheduled Monthly EMI: $0
Principal Reduction: Prepaying $0 lowers balance in Month 12.
New Loan Term: Payoff accelerated by 0 months.

Amortization Schedule

Interactive breakdown of balance, interest, and prepayment impact

Period	EMI Paid	Principal Paid	Extra Prepayment	Interest Paid	Total Payment	Remaining Balance

How Prepayment Interest Is Calculated on Reducing-Balance Loans

Understanding the math behind loan amortization shows why even small extra contributions create disproportionate savings. Every billing cycle, your lender multiplies your remaining principal balance by the periodic interest rate before applying the rest of your installment toward principal. When you pay extra directly toward principal using our Extra Principal Payment Calculator, that reduced principal stops accruing interest for every single remaining month of your tenure.

If you plan to deploy an annual bonus, explore the Lump Sum Prepayment Calculator, or compare recurring additions with the 1 Extra EMI Per Year Calculator and Bi-Weekly Mortgage Calculator. Before locking in a strategy, check whether any lender fee applies using our Prepayment Penalty Calculation Guide, or compare prepaying debt against market investing with the Prepay vs. Invest Calculator inside the Extra Payment & Strategy Hub.

Frequently Asked Questions

How is prepayment interest calculated on loans?

Most banks calculate interest on a Daily Reducing Balance basis. The daily interest formula is: Daily Interest = (Outstanding Principal × Annual Interest Rate) ÷ 365. When you make a prepayment, the outstanding principal immediately drops. Model live reducing-balance savings in our Prepayment Savings Calculator or Extra Principal Payment Calculator.

Does prepayment go towards interest or principal first?

When an EMI is paid, it first covers the accrued monthly interest, with the remaining portion reducing principal. However, when you make a dedicated part-prepayment, 100% of that extra amount goes directly to reducing the principal balance—read full servicing rules in What Is an Extra Principal Payment? or Prepayment Amount Meaning.

What is the formula to calculate interest saved from prepayment?

Total Interest Saved = Total Scheduled Interest (Original) - Total Revised Interest (After Prepayments). Explore step-by-step principal curtailment equations in How to Calculate Extra Principal Payments and Compounding Time Effect Guide.

Is interest calculated monthly or daily on mortgages?

In modern retail banking (including India, US, UK, Australia, and Canada), interest is accrued daily based on the day's closing principal balance and debited monthly. Check daily offset benefits in our Mortgage Offset Account Calculator or bank-specific rules in Global Bank Presets.