How to Calculate a Loan Payment, Total Interest and Payoff Date

To calculate a loan payment, open the Loan Calculator and enter the Loan amount, Annual interest rate % and Term (years) — it returns the monthly payment instantly, along with total interest, the payoff date, and how much of your first payment goes to interest versus principal.

What the Loan Calculator does

A loan payment isn't just the amount borrowed divided by the number of months — interest compounds every period, so the calculator applies the standard amortization formula to turn a loan amount, rate and term into a fixed monthly payment. It then breaks that payment down further: how many payments you'll make in total, how much of the loan's total cost is interest versus principal, and the exact date of your final payment based on when you make your first one.

How to calculate a loan payment with Toolbench

1. Open the Loan Calculator.
2. Enter the Loan amount you're borrowing.
3. Enter the Annual interest rate % (the loan's APR or stated rate).
4. Enter the Term (years) — the calculator converts this to a number of monthly payments automatically.
5. Optionally set First payment — it defaults to today's date, and is used to compute the payoff date.
6. Read the Monthly payment in the large result box, then check the rows below for the number of payments, total paid, total interest, interest share, the interest/principal split of your first payment, and the payoff date.

Example: a $25,000 loan at 6.5% over 5 years

The tool opens with these defaults:

Loan amount	25,000
Annual interest rate %	6.5
Term (years)	5
Monthly payment	489.15
Number of payments	60
Total paid	29,349.22
Total interest	4,349.22
Interest share	14.82%
First payment: interest / principal	135.42 / 353.74

Borrowing 25,000 at 6.5% over 60 months costs 489.15 a month, 29,349.22 in total — meaning 4,349.22, or 14.82% of everything you pay, is interest rather than principal. On the very first payment, 135.42 goes to interest and only 353.74 actually reduces the balance; that split shifts toward principal with every payment as the balance shrinks.

Example: a 0% loan

Set the rate to 0 and the formula drops out entirely — the calculator just divides the loan amount by the number of payments. A $15,000 loan at 0% over 3 years (36 payments) comes out to exactly 416.67 a month, 15,000.00 total paid, and 0.00 interest. This is the case to check when comparing a 0%-APR financing offer against a loan that carries interest.

Why the interest/principal split matters

Early payments on any amortizing loan are interest-heavy because interest is charged on the full remaining balance each period. In the 6.5% example above, interest is 135.42 of the very first 489.15 payment — over a quarter of it — even though the loan's overall interest share is only 14.82%. That gap narrows every month as the balance drops, which is why paying extra early in a loan's term saves more interest than paying extra near the end.

Tips and common mistakes

• Use the loan's stated annual rate, not a monthly one. The calculator expects the annual rate and converts it to a monthly rate internally (dividing by 1,200) — entering a monthly rate will produce a payment far too high.
• Term is always converted to months. A 5-year term becomes 60 monthly payments; a 2.5-year term becomes 30. Fractional years are rounded to the nearest whole month.
• "Interest share" is relative to the total paid, not the loan amount. 14.82% in the example means interest is 14.82% of everything you'll pay (29,349.22), not 14.82% of the 25,000 borrowed.
• The payoff date depends on your First payment date. Change it from today's default to your loan's actual first due date to get an accurate final payment date.
• A 0% rate still works. With no interest, the payment is just the loan amount divided by the number of payments, and total interest comes out to zero.

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Frequently asked questions

How is a monthly loan payment calculated?

It uses the standard amortization formula: payment = P × i ÷ (1 − (1 + i)⁻ⁿ), where P is the loan amount, i is the monthly interest rate (annual rate ÷ 1,200), and n is the number of monthly payments. If the rate is 0%, the payment is simply the loan amount divided by the number of payments.

Why is so much of my first payment interest?

Interest is charged on the remaining balance each period, and the balance is at its highest right at the start of the loan. As you pay down principal, the interest portion of each payment shrinks and the principal portion grows, even though the total payment stays the same.

What does "Interest share" mean on the Loan Calculator?

It's total interest divided by total paid, expressed as a percentage — it tells you what fraction of everything you'll pay over the life of the loan is interest rather than principal, as opposed to interest as a fraction of the original loan amount.

Does the calculator account for extra payments or fees?

No. It calculates a standard fixed-rate, fixed-term amortization schedule from the loan amount, rate and term you enter — it doesn't factor in origination fees, extra principal payments, or variable rates.

Is my loan information sent to a server?

No. The calculation happens in your browser as you type. If you're signed in, your inputs sync privately to your account; if you're signed out, nothing is saved anywhere.