Loan Calculator — Monthly Payment & Amortization Schedule

Guide

About Loan Calculator

Compute monthly loan payment and a full amortization schedule. Enter principal, annual interest rate, and term (months or years). Get the payment, the total interest paid, and a period-by-period table showing principal vs interest. Useful for mortgage shopping, refinance comparison, and overpayment modeling.

What the schedule reveals

A 30-year fixed mortgage at 6.5% on $400,000:

Monthly payment: $2,528
Total paid over 30 years: $910,178
Total interest: $510,178

Surprising on a first read. Interest equals 1.27× the principal. The schedule shows that for the first 10 years, ~70% of each payment is interest. By year 20, the balance flips.

Common workflows

Mortgage shopping. Compare 15- vs 30-year, fixed rates from different lenders. Total interest is the headline number.

Refinance decision. Plug current loan, plug refinance terms, compare total remaining interest. Subtract closing costs to find the break-even.

Extra payment impact. Adding $200/month to a 30-year mortgage knocks years off and saves tens of thousands in interest. The schedule shows the new payoff date.

Auto loan. Same math, shorter term. 5-year auto loans amortize fast.

Why a tool

Banks compute these on request, but their numbers come back days later. The tool gives an answer in seconds — useful for negotiation, sanity-checking the lender’s quote, and modeling “what if I pay extra”.

Frequently asked questions

How is monthly payment calculated?

Standard amortization formula — P × [r(1+r)^n] / [(1+r)^n - 1] where P is principal, r is the monthly rate, n is the number of payments. The tool plots the formula's output verbatim.

Why does interest dominate early payments?

Interest accrues on the remaining balance. Early in the loan, balance is high → most of your payment goes to interest. Late in the loan, balance is low → most goes to principal.

Extra payments?

Toggle Extra payment to add a flat amount to each payment. Reduces total interest dramatically.

15-year vs 30-year mortgage?

15-year doubles principal payment but cuts total interest dramatically. The schedule shows the tradeoff visually.

ARM (adjustable rate)?

Not modeled — assume fixed rate. For ARM modeling, run multiple fixed-rate scenarios for each rate period.

APR vs rate?

APR includes fees; rate is just interest. Use APR for comparison shopping. We accept either.

Does it work for car, auto, student, and personal loans?

Yes — a car, auto, student, personal, or business loan is the same amortization math as a mortgage, just with a different principal, rate, and term. Enter your numbers and the tool gives the monthly payment, total interest, and full schedule regardless of loan type. Only exotic structures (interest-only periods, ARMs, income-driven student plans) need special handling.

How long will it take to pay off my loan?

That depends on the payment. Enter the principal, rate, and your planned monthly payment, and the amortization schedule shows the payoff date. Adding even a small extra payment each month shortens the term noticeably — toggle it on to see how many months and how much interest you save.

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Last updated: 2026-07-04