Loan Payment Calculator

How to Use the Loan Payment Calculator

Three inputs produce the payment, and the payment is only half the story. The other half is the amortisation schedule underneath it, which is where you can see how little of an early payment actually reduces what you owe.

1. Enter the loan amount. The sum actually advanced to you. If fees are being added to the loan rather than paid up front, include them here — that is how the lender will treat them.
2. Enter the annual rate. Use the APR if you have it, since it already reflects most fees. If you only have a nominal rate and there are arrangement fees, the APR calculator converts between the two.
3. Enter the term in years. Decimals work: 3.5 for forty-two months. Term is the input with the most counter-intuitive effect — it lowers the payment and raises the total cost at the same time.
4. Open the schedule. The table summarises each year: principal paid, interest paid, and the balance still outstanding. It is the most useful part of the page and the part most calculators leave out.

The fourth tile shows how much of your very first payment is interest rather than principal. On a five-year loan at 7.5% it is about 31%; on a thirty-year mortgage at the same rate it is closer to 80%. That single figure explains why long loans feel like they never move.

Loan Payment Formula

This is the standard amortising loan formula, sometimes called the annuity payment formula. It finds the constant payment that reduces the balance to exactly zero at the end of the term.

Every month, interest is charged on whatever is still outstanding, and the rest of your payment reduces the balance. Because the balance falls, the interest portion falls too and the principal portion rises — which is why the schedule accelerates towards the end even though the payment never changes.

Example

$25,000 at 7.5% APR over five years

1. Monthly rate: 0.075 ÷ 12 = 0.00625. Payments: 5 × 12 = 60.
2. Denominator: 1 − 1.00625⁻⁶⁰ = 1 − 0.688092 = 0.311908.
3. Payment: 25,000 × 0.00625 ÷ 0.311908 = 156.25 ÷ 0.311908 = $500.95 a month.
4. Total repaid: 500.95 × 60 = $30,056.92.
5. Total interest: 30,056.92 − 25,000 = $5,056.92, which is 20.23% of the amount borrowed.
6. First payment: interest is 25,000 × 0.00625 = $156.25, so only $344.70 reduces the balance — 68.8% of the payment.

The same loan over three, five and seven years

Stretching from three years to seven cuts the monthly payment in half and more than doubles the interest. Neither column is the right answer on its own: the three-year payment is only better if you can actually afford it every month for three years, and a missed payment costs more than the interest saved.

Reading the Amortisation Schedule

The schedule is where a loan reveals itself. Here is how the split moves on the worked example.

Interest falls by a fifth in the first year and faster after that, while the payment never changes. By year five about 96% of every payment is reducing the balance rather than paying for the privilege of owing it. That is the mechanism behind every piece of advice about overpaying early: money paid in year one removes interest from all sixty months, and money paid in year five removes it from almost none.

The interest-share tile is a quick sanity check on any loan offer. Around 20% of principal over five years is unremarkable for unsecured consumer credit. If a calculation shows total interest approaching or exceeding the amount borrowed, either the rate is very high, the term is very long, or both — and it is worth asking whether the purchase justifies it.

There is one more reading worth taking from the schedule. Add up the interest column for the first half of the term and compare it with the second half: on this loan, roughly two-thirds of all the interest is paid in the first thirty months. Any decision that shortens the loan early — a lump sum, a higher payment, refinancing onto a shorter term — is acting on the expensive half. The same decision taken in year four is acting on almost nothing, which is why timing matters as much as amount.

Where a Real Loan Differs From This Model

Four things that make a real loan differ from this model.

Fees. Arrangement fees, documentation fees and broker commissions may be charged up front, added to the loan, or both. A $500 fee on a $25,000 loan is worth about 0.4 percentage points of APR over five years — enough to change which of two offers is cheaper.

Day-count conventions. This calculator uses twelve equal months, which is what most consumer lenders quote. Some use actual days over 365, which produces a slightly different figure — usually a few pounds over the life of a loan, occasionally more on large balances.

Early repayment. Many agreements allow overpayment; some charge for it. On this loan, an extra $100 a month clears the balance about eleven months early and saves roughly $1,000 in interest. Check the agreement for an early settlement charge before assuming that saving is available.

Variable rates. The model assumes a fixed rate for the whole term. If your rate tracks a benchmark, run the calculation at your current rate and again two points higher, and check the higher payment still fits your budget.

For a mortgage specifically, use the mortgage calculator instead — it adds property tax, insurance, HOA dues and private mortgage insurance to the principal-and-interest figure this page produces, and those additions often exceed 25% of the real monthly cost. For a revolving balance rather than a fixed-term loan, the credit card interest calculator models the declining minimum payment properly.