What Is a Loan & Mortgage Calculator?
The Loan & Mortgage Calculator shows the fixed monthly payment for a loan, how much interest you pay in total, and a year-by-year amortization schedule.
A loan calculator works out the fixed monthly payment for an amortising loan — a mortgage, car loan or personal loan — along with the total interest you will pay and a schedule showing how the balance falls over time. It turns the three numbers you know (amount borrowed, interest rate and term) into the one number you really need: what it costs each month, and overall.
How the Monthly Payment Is Calculated
The fixed payment comes from the amortisation formula M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the loan amount, r the monthly interest rate (the annual rate divided by 12) and n the number of monthly payments. Each month part of the payment covers interest on the remaining balance and the rest reduces the principal.
Early on, most of each payment goes to interest because the balance is large; as the balance shrinks, more of every payment chips away at the principal. The amortisation schedule lays this out period by period, which is why the total interest can be a surprisingly large share of the loan over a long term.
What the monthly payment doesn't tell you
Comparing nominal rates instead of the total cost
The advertised rate leaves out arrangement fees, mandatory insurance and registration costs, all of which are commonly financed into the balance. Two loans at the same nominal rate can differ by thousands once those are included. Compare the total amount payable over the full term, which is the number this calculator puts next to the payment.
Choosing the longest term because the payment is lowest
Stretching the term always reduces the monthly figure and always increases what you hand over. In the table below, moving from ten years to thirty cuts the payment by about a third and more than triples the interest. That trade can still be the right call for cash flow — but it should be a decision, not a default.
Not realising how little early payments touch the principal
In a standard amortising loan every instalment is the same size, but its composition is not. Early on, most of it is interest on a balance that has barely moved; the principal share climbs slowly and only overtakes interest well into the term. This is why leaving in the first years feels like paying for nothing.
Making extra payments without directing them
An overpayment can reduce the outstanding balance or simply cover future instalments, and lenders do not always default to the first. Only the balance reduction shortens the loan and saves interest. Whenever you overpay, state explicitly that it goes against the principal and confirm the term was recalculated.
The cost of a longer term
Same loan of 200,000 at 9% a year, amortised monthly. Only the term changes.
| Term | Monthly payment | Total paid | Interest | Interest vs principal |
|---|---|---|---|---|
| 10 years | 2,534 | 304,022 | 104,022 | 52% |
| 15 years | 2,029 | 365,136 | 165,136 | 83% |
| 20 years | 1,799 | 431,868 | 231,868 | 116% |
| 30 years | 1,609 | 579,328 | 379,328 | 190% |
Between the twenty and thirty year rows the payment falls by about 190 a month while the interest rises by roughly 147,000. Long terms buy breathing room at a price that is easy to miss when only the monthly figure is on the table.
Loan Data Stays Private
Loan payments are computed using amortization formulas as JavaScript code running in your browser. Your principal amount, interest rate, and term are calculated locally on your device — this financial data never reaches our servers.