Loan Payments Explained: Where Your Monthly Payment Goes

You borrow money, agree to repay it in equal monthly payments, and the lender tells you the amount. But what is inside that payment? Why does the balance barely fall in the first year? And what happens if you pay a bit extra? Understanding the mechanics helps you choose a better loan and save real money.

What a payment is made of

Every payment on a standard instalment loan has two parts. The interest part pays for the use of the money since the last payment: the outstanding balance times the monthly rate. Whatever is left of the payment goes to principal, which is the amount you actually borrowed. Because interest is charged on the balance, and the balance is highest at the start, early payments are mostly interest.

Take $25,000 borrowed at 6 percent for five years. The monthly payment is $483.32. In the first month, interest is $25,000 × 0.005 = $125, so only $358.32 reduces the balance. By the last payment, interest is only about $2.40 and nearly the whole amount goes to principal. The payment never changes, but its make-up shifts every month.

How the payment is calculated

The payment is chosen so that the balance reaches exactly zero after the last instalment. The formula is payment = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the loan amount, r is the monthly rate (the yearly rate divided by 12) and n is the number of payments. If the rate is zero, the payment is simply P ÷ n.

You do not need to do this by hand, but it explains something useful: the payment depends on three things only, the amount, the rate and the number of months. Change any one and the payment moves in a predictable way.

Term: cheaper each month or cheaper overall

For the $25,000 loan at 6 percent:

• Three years: $760.55 a month, $2,379.74 of interest
• Five years: $483.32 a month, $3,999.20 of interest
• Seven years: $365.21 a month, $5,677.96 of interest

Stretching the loan from three to seven years lowers the payment by almost $400 a month but more than doubles the interest. A longer term is not wrong, it can make a loan affordable, but it is a decision to pay for that relief with extra interest. Choose the shortest term whose payment you can keep up comfortably.

The power of an extra payment

Extra money goes to principal, so the balance falls faster and every later month's interest is smaller. Adding $100 a month to the five-year loan clears it in 49 months instead of 60 and reduces the interest from $3,999.20 to $3,206.27, a saving of $792.93. The extra payments total about $4,900 over the shorter period, but you get most of that back in avoided interest.

APR versus the interest rate

The interest rate is the yearly price of the money. The APR adds certain fees, such as origination charges, to give a single comparable figure. Two loans with the same rate can have very different costs if one charges a fee. Compare loans by their APR and by the total you will repay, not just the monthly payment.

Fixed and variable rates

With a fixed rate, the payment never changes, which makes budgeting easy. With a variable rate, the payment can rise when rates rise. The calculators on this site assume a fixed rate, so treat the results for a variable loan as a snapshot and recalculate when the rate changes.

Checklist before you sign

• Write down the amount, APR, term, monthly payment and total repayment, and check they agree.
• Ask about origination, late and prepayment fees.
• Check whether insurance or other add-ons are being included in the loan.
• Compare at least three offers, including one from a credit union or bank you already use.
• Make sure the payment leaves room for your other fixed costs and an emergency fund.

Run your own numbers

The Loan Calculator shows the payment, the total interest, a payoff chart and a year-by-year or month-by-month schedule, and it compares an extra monthly payment with the standard plan. For a car loan with tax and a trade-in, use the Car Payment Calculator. If your payment is quoted as an EMI, try the EMI Calculator, and for a home loan the Mortgage Calculator. If credit cards are part of your debt, the Credit Card Payoff Calculator shows how quickly you could clear them.