Repayment Calculator

Repayment Calculator

Calculate the monthly payment, total interest, and a yearly amortization summary for any fixed-rate loan.

Monthly Payment
—
Total paid over loan term—
Total interest paid—
Payoff time with extra payment—
Interest saved with extra payment—
YearPrincipal PaidInterest PaidRemaining Balance
Disclaimer: This calculator provides estimates for general educational and planning purposes only and does not constitute financial advice. Actual loan terms, fees, and repayment schedules are set by your lender. Consult your loan provider or a financial advisor for exact figures.

Repayment Calculator: How to Calculate Loan Payments and Payoff Time

Quick summary: A repayment calculator uses the amortization formula — Payment = P × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1) — to determine your fixed monthly payment on a loan, then tracks how each payment splits between principal and interest over time. Adding even small extra payments can meaningfully cut both your total interest and payoff timeline, since every extra dollar reduces the principal balance that future interest is calculated on.

Whether you’re financing a car, taking out a personal loan, or paying down a mortgage, a repayment calculator shows you exactly what you’ll owe each month — and just as importantly, how much of that payment is actually going toward your balance versus disappearing into interest. This guide breaks down the amortization formula behind every repayment calculator, walks through fully worked examples, and explains why extra payments made early in a loan save dramatically more than the same extra payments made later.

What Is a Repayment Calculator?

A repayment calculator estimates your fixed periodic loan payment using a standard amortization formula that combines the total loan principal, the interest rate converted to a periodic rate, and the total number of payments over the loan’s term (best-calculators.com). Amortization itself is the process of gradually repaying a loan through scheduled payments that cover both principal and interest — with a fixed-rate loan, your monthly payment amount stays constant, but the mix of principal and interest inside that payment shifts over time (transunion.com).

The Repayment Calculator (Amortization) Formula

The standard formula used by essentially every repayment calculator is:

Payment = P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1)

Where:

  • P = the loan principal (amount borrowed)
  • r = the monthly interest rate (annual rate ÷ 12)
  • n = the total number of monthly payments (loan term in years × 12)

(ultimatefinancecalculator.com)

Converting an Annual Rate to a Monthly Rate

TransUnion’s amortization guidance walks through this conversion directly: for a 9.0% annual interest rate, divide by 12 to get the monthly rate: 9.0% ÷ 12 = 0.75%, or 0.0075 as a decimal. For a 30-year loan, multiply the years by 12 to get the total number of monthly payments: 30 × 12 = 360 payments (transunion.com).

How Each Payment Splits Between Principal and Interest

Every month, a repayment calculator recalculates the split using this logic:

Interest for the month = Remaining Balance × Monthly Rate Principal Reduction = Monthly Payment − Interest New Balance = Remaining Balance − Principal Reduction

(ultimatefinancecalculator.com)

Because interest is calculated on the remaining balance, early payments on a loan are interest-heavy, while later payments become increasingly principal-heavy — the total payment stays the same, but its internal makeup shifts steadily toward principal as the balance shrinks (usbank.com).

Worked Examples

Example 1: Standard loan payment calculation

You borrow $20,000 at a 6% annual interest rate over 60 months (5 years).

Step 1 — Convert to monthly rate: r = 0.06 ÷ 12 = 0.005 Step 2 — Apply the formula:

Payment = 20,000 × 0.005 × (1.005)⁶⁰ ÷ ((1.005)⁶⁰ − 1) ≈ $386.66/month

Example 2: Adding a small extra payment

Using the same $20,000 loan at 6% over 60 months, you add $50/month extra starting from your first payment.

According to Ultimate Finance Calculator’s worked example on this exact scenario, adding $50 extra per month saves $429.04 in interest and pays off the loan 7 months early — reducing total payments from $23,199.36 down to $22,770.33 (ultimatefinancecalculator.com). The loan also pays off in 53 months instead of 60.

Example 3: A larger mortgage, extra payment impact

A homeowner has a $300,000 mortgage at 6.5% over 30 years, with a base monthly payment of $1,896.20.

If they add $200/month in extra payments starting from month 1, they save $103,449 in interest — a 187% return, or $1.87 saved for every $1 of extra payment (ultimatefinancecalculator.com). Doubling that extra payment to $400/month would save $159,832 and shorten the loan by 132 months total.

Example 4: Why timing matters — early vs. late extra payments

According to Total Mortgage’s extra payment guidance, a $10,000 lump-sum extra payment applied in the first years of a mortgage saves the most interest, because that’s when the largest share of each standard payment is going toward interest rather than principal. The same $10,000 applied in year 20 of the same loan saves only a fraction of that amount, since by then most of the loan’s total interest has already been paid (totalmortgage.com).

Three Ways to Pay Off a Loan Faster (And How They Differ)

These strategies are often confused, but according to Total Mortgage, they solve genuinely different problems:

  • Extra payments — shorten your loan term and reduce total interest paid, but your required minimum monthly payment stays exactly the same. Best when your goal is becoming debt-free sooner while comfortably affording your current payment (totalmortgage.com).
  • Biweekly payments — paying half of your monthly payment every two weeks results in 26 half-payments per year, which works out to 13 full payments instead of the usual 12. That one extra annual payment meaningfully reduces both payoff time and total interest cost (best-calculators.com).
  • Loan/mortgage recasting — after making a large lump-sum principal payment, your lender re-amortizes the loan, which lowers your required monthly payment going forward while keeping your original interest rate and general payoff structure intact (totalmortgage.com).

Why Extra Payments Compound Into Big Savings

The mechanism is simple but powerful: since interest is calculated on your remaining balance each period, every extra dollar you pay goes straight to principal, which permanently lowers the balance that future interest gets calculated against (totalmortgage.com; ultimatefinancecalculator.com). This creates a compounding effect — a smaller balance means less interest next month, which means slightly more of next month’s payment goes to principal, and so on, snowballing over the life of the loan.

FAQs

How is a monthly loan payment calculated?

A monthly loan payment is calculated using the amortization formula, which combines the loan principal, the monthly interest rate (annual rate divided by 12), and the total number of payments over the loan term.

Do extra payments lower my required monthly payment?

No — regular extra payments shorten your loan term and reduce total interest paid, but your required minimum monthly payment stays the same, unless your lender specifically recasts the loan after a large lump-sum payment.

When is the best time to make extra payments on a loan?

Extra payments made earlier in a loan’s term save significantly more interest than the same extra payments made later, because a larger share of early payments goes toward interest rather than principal.

Does paying biweekly instead of monthly actually save money?

Yes — paying half your monthly payment every two weeks results in 13 full payments per year instead of 12, which reduces both your total interest cost and your overall payoff timeline.

What’s the difference between extra payments and loan recasting?

Extra payments shorten your loan term while your required payment stays the same. Loan recasting keeps your original term and rate but lowers your required monthly payment after a large lump-sum principal payment, since the lender re-amortizes the loan around the new, smaller balance.

Related Calculators

Conclusion

A repayment calculator takes the amortization formula — principal, interest rate, and term — and turns it into a clear monthly payment figure, plus a full picture of how that payment splits between principal and interest over the life of your loan. Understanding how extra payments compound, why timing matters so much, and how strategies like biweekly payments and loan recasting differ will help you use a repayment calculator not just to see what you owe, but to actually pay it off faster and cheaper.