Loan & Mortgage Calculator

What is a loan and mortgage calculator?

A loan calculator turns three inputs — how much you borrow, the interest rate, and how long you take to repay — into the numbers that actually shape your budget: the monthly payment, the total interest over the life of the loan, and the grand total you'll repay. For a mortgage, a car loan, a personal loan or a student loan, the maths is identical; only the figures change.

The tool above does more than spit out a single number. It builds the complete amortization schedule — a row for every payment — so you can see exactly how each instalment is split between interest and principal, and watch the balance fall to zero. It also has an extra payment field: type in an additional amount each month and it recalculates a new, earlier payoff date and tells you how much interest you've just saved.

Everything runs in your browser. Loan figures are personal, so nothing you enter is uploaded or stored — the calculation happens entirely on your own device, instantly, as you type.

How to use it

1. Enter the loan amount. This is the principal — the sum you're borrowing, after any deposit or down payment.
2. Enter the annual interest rate. Use the rate quoted by the lender (the nominal APR works fine here). For a 5.5% loan, type 5.5.
3. Set the term and choose years or months with the toggle. A 30-year mortgage is 30 years; a 48-month car loan is 48 months.
4. Optionally add an extra monthly payment. Leave it blank for the standard schedule, or enter an amount to see the accelerated payoff.
5. Read the results. The headline shows your monthly payment; the cards below show principal, total interest and total paid. Scroll the amortization table to see every payment, and use Copy to grab a one-line summary.

The amortization formula explained

The monthly payment on a fixed-rate, fully amortizing loan comes from one formula:

M = P · r · (1 + r)^n ÷ ((1 + r)^n − 1)

• M is the monthly payment.
• P is the principal (the loan amount).
• r is the monthly interest rate — the annual rate divided by 12, then by 100. A 6% annual rate gives r = 0.06 ÷ 12 = 0.005.
• n is the total number of monthly payments — years × 12.

Once M is known, each month's split is easy. The interest part of a payment is the current balance × r. The principal part is whatever is left of M after the interest. Subtract that principal from the balance, and you have the figure to start the next month with. Repeat n times and the balance reaches zero exactly on the final payment — that's what "amortizing" means.

This is why the schedule looks the way it does. At the start, the balance is large, so most of each payment is eaten by interest and only a sliver pays down the debt. As the balance shrinks, the interest portion falls and the principal portion grows, accelerating toward the end. The payment never changes, but what it's doing changes every single month.

A worked example

Suppose you borrow $250,000 at 5.5% annual interest over 30 years (360 months).

• Monthly rate: 5.5 ÷ 12 ÷ 100 = 0.0045833
• Payments: 30 × 12 = 360
• Plugging into the formula gives a monthly payment of about $1,419.47.

Over the full term you'd pay 360 × 1,419.47 ≈ $511,010, of which the original $250,000 is principal and roughly $261,010 is interest. On a long mortgage, the interest can rival or exceed the amount you borrowed — a striking fact the schedule makes impossible to ignore.

Look at the first payment in that schedule: interest is 250,000 × 0.0045833 ≈ $1,145.83, leaving only about $273.64 to reduce the balance. By the final year, almost the entire payment is principal. Seeing that shift is the single most useful thing an amortization table does.

How extra payments save interest

Here's the lever most borrowers underuse. Because interest is charged only on the remaining balance, any extra principal you pay today erases every future interest charge that balance would have produced. The earlier you do it, the more it compounds in your favour — the same compounding that grows your money in a compound interest calculator, only this time working for you instead of the lender.

Take the $250,000 example and add just $200 a month. That extra principal pulls the balance down faster, so the loan clears years ahead of schedule and you avoid tens of thousands in interest you'd otherwise have paid. The calculator's extra-payment callout shows the exact new payoff time and the interest saved for your figures.

A few practical notes:

• Front-loaded benefit. Extra payments in year one save far more than the same payments in year twenty, because there's more interest left to cancel.
• Check for penalties. Some loans charge a prepayment penalty. Most modern mortgages don't, but confirm before you commit a strategy to it.
• Tell the lender it's principal. Make clear that extra money should reduce the principal, not just sit as a prepaid future instalment, or you may not get the saving.

Fixed vs variable rates

This calculator models a fixed-rate loan: the rate, and therefore the payment, stays the same for the whole term. That's the cleanest case and the right model for most mortgages and personal loans quoted at a single rate.

A variable (or adjustable) rate changes over time, usually tracking a benchmark. When the benchmark rises, your payment rises; when it falls, you pay less. Variable loans often start with a lower "teaser" rate, which can make the early payments look attractive — but the schedule will shift whenever the rate resets. Use this tool to model a variable loan by running it at the current rate, then again at a higher rate, to see your exposure if rates climb. Treat the gap between those two scenarios as your risk budget.

Tips for borrowing smarter

• Shorten the term if you can afford it. A 15-year mortgage costs more per month than a 30-year one but saves enormous interest. Compare both in the calculator side by side.
• Watch the total, not just the monthly. A lower monthly payment achieved by stretching the term often means paying far more interest overall. The "total paid" figure tells the real story, and a percentage calculator makes it easy to see what share of that total is pure interest.
• Round up your payment. Even paying to the next clean number each month behaves like a small permanent extra payment.
• Re-run it when rates move. If you're offered a refinance, model the new rate and remaining balance here before deciding — sometimes the fees outweigh the saving.

Private, instant and always free

This loan and mortgage calculator runs entirely in your browser. There are no accounts, no limits, and your figures never leave your device. Keep it bookmarked for the next quote you're handed — it turns an amount, a rate and a term into a clear payment, a full schedule, and a concrete plan for paying less interest, while your numbers stay yours.