Mortgage Calculator
Calculate monthly payments, total interest and amortization
100% free. Runs entirely in your browser - your files and data never leave your device and nothing is uploaded to any server.
Monthly payment here is principal, interest, property tax and insurance. UK, Welsh, Scottish and Australian buyers also pay stamp or transfer duty at purchase — that is not in this figure. Estimate stamp duty.
| # | Payment | Principal | Interest | Balance |
|---|---|---|---|---|
| 1 | $1,517 | $217 | $1,300 | $239,783 |
| 2 | $1,517 | $218 | $1,299 | $239,565 |
| 3 | $1,517 | $219 | $1,298 | $239,346 |
| 4 | $1,517 | $221 | $1,296 | $239,125 |
| 5 | $1,517 | $222 | $1,295 | $238,903 |
| 6 | $1,517 | $223 | $1,294 | $238,680 |
| 7 | $1,517 | $224 | $1,293 | $238,456 |
| 8 | $1,517 | $225 | $1,292 | $238,231 |
| 9 | $1,517 | $227 | $1,290 | $238,004 |
| 10 | $1,517 | $228 | $1,289 | $237,777 |
| 11 | $1,517 | $229 | $1,288 | $237,548 |
| 12 | $1,517 | $230 | $1,287 | $237,317 |
About this tool
A mortgage payment is fixed, but what it buys changes every month. Early on, almost all of it is interest and barely any touches the balance - on a typical 30-year loan the first payment might be 80% interest. That ratio slowly inverts, and only in the final years does most of each payment reduce what you owe. This is amortisation, and understanding it explains the single most consequential number in the whole arrangement: total interest paid. Borrow at 6% over 30 years and you can easily repay close to double what you borrowed. The same loan over 15 years costs a higher monthly payment but dramatically less overall, because there are fewer years for interest to accrue. That trade-off - monthly affordability against lifetime cost - is what this calculator exists to make visible. Note it computes principal and interest only; property taxes, insurance and service charges are additional. Calculations run in your browser.
How to use this tool
- Enter the loan amountThe property price minus your deposit - what you are actually borrowing, not what the house costs.
- Enter the interest rate and termThe annual rate, and the length in years. 15 and 30 are the common comparison points.
- Read the monthly paymentThis is principal and interest. Taxes, insurance and any service charge sit on top.
- Look at the total interest, not just the monthly figureThis is where the real difference between options appears, and it is the number most people never check.
How a monthly mortgage payment is calculated
The standard formula is M = P x r x (1 + r)^n / ((1 + r)^n - 1), where P is the loan amount, r the monthly interest rate (the yearly rate divided by 12) and n the number of monthly payments. A 300,000 loan at 6% over 30 years has r = 0.005 and n = 360, which gives a payment of about 1,799 a month before tax and insurance.
Over the full term that loan costs about 647,500, so roughly 347,500 is interest. In the first month, 1,500 of the 1,799 is interest - over 80% - which is why the amortization schedule shows the balance falling slowly at first and much faster in the later years.
Key features
- Shows total interest over the loan, which is the figure that actually distinguishes one mortgage from another.
- Full amortisation breakdown, so you can see how the principal and interest split shifts over time.
- Compare terms and rates side by side before committing.
- Runs in your browser - your financial details are never transmitted.
- No account and no lead capture.
Common uses
- Working out what you can realistically afford before house-hunting.
- Comparing a 15-year against a 30-year term to see the lifetime cost difference.
- Checking how much a quoted rate difference is actually worth over the full term.
- Estimating the effect of a larger deposit on both payment and total cost.
- Sanity-checking a lender's figures before signing.
Tips for better results
- Compare total interest, not monthly payment. A lower monthly figure over a longer term usually costs far more overall.
- Try a small overpayment. Even a modest amount each month, applied to principal, can remove years from the term and a large sum from the total interest.
- Budget for taxes, insurance and maintenance separately - the true monthly cost of owning is well above principal and interest.
- Half a percentage point sounds trivial and is not. Run both rates through and look at the total.
- Check whether overpayments are permitted without penalty before relying on them in your plan.
Mistakes to avoid
- Judging affordability on the monthly payment alone, ignoring the total cost of the loan.
- Forgetting that taxes and insurance are additional, then finding the real payment is significantly higher.
- Choosing the longest term automatically for the lowest payment, without seeing what it costs across the full period.
- Entering the property price rather than the loan amount, which inflates every figure.
- Assuming rates and payments are fixed for the whole term when the product is variable or fixed for only an initial period.
Available options
- Loan amount
- Rate
- Term
- Monthly payment
Frequently asked questions
A breakdown showing how each monthly payment splits between principal and interest over the life of the loan - early payments are mostly interest, while later payments are mostly principal, even though the total payment stays the same.
This calculates the core principal-and-interest payment based on loan amount, rate, and term - real-world mortgage payments often also include property taxes, insurance, and HOA fees, which aren't part of this base calculation unless you factor them in separately.
Yes, and you should. Run 15 and 30 years side by side and compare total interest rather than the monthly figure - the difference over the life of the loan is usually far larger than people expect.
Because interest is charged on the outstanding balance, which is at its largest at the start. As the balance falls, the interest portion falls with it and more of each fixed payment reduces the principal. That is amortisation, and it is why overpaying early has a disproportionate effect.
More than most people assume. Every extra amount applied to principal removes all the future interest that balance would have accrued, so consistent modest overpayments can cut years off the term. Check your lender permits them without penalty first.
No. Everything is calculated in your browser and nothing is transmitted, saved or used for lead generation.
Lenders commonly ask for 5-20% of the price. A larger deposit lowers the loan-to-value ratio, which usually unlocks a lower rate; in the US, under 20% down on a conventional loan typically means paying private mortgage insurance (PMI).
A 15-year loan has a higher monthly payment but a lower rate and far less total interest. A 30-year loan keeps payments low and flexible. Compare both here: the difference in total interest is often larger than people expect.
On a 300,000 loan over 30 years, moving from 6% to 7% raises the monthly payment by roughly 200 and the total interest by about 70,000. Enter your own figures to see the effect on your loan.