Mortgage calculator
Enter the home price, your down payment (deposit), the interest rate and the term. The mortgage calculator gives you the loan amount, loan-to-value, monthly payment, total interest and a year-by-year amortization schedule. Compare a standard repayment mortgage with equal-principal and interest-only loans and see what extra payments save. Works in any currency, nothing leaves your browser.
Source: Consumer Financial Protection Bureau – What is amortization and how could it affect my loan?. Updated: .
How it is calculated
How the mortgage calculator works
The loan amount is the home price minus your down payment. Interest is charged monthly on the outstanding balance (annual rate ÷ 12) and rounded to the cent. The calculator supports three repayment types:
- Repayment mortgage (amortizing): the same payment every month, P = L · r · (1 + r)n ÷ ((1 + r)n − 1) with r = annual rate ÷ 12 and n = number of payments. Early payments are mostly interest; the principal share grows over time.
- Equal principal: the same amount of principal every month (loan ÷ months), so the payment starts higher and falls as interest shrinks.
- Interest-only: you pay only the interest and repay the whole loan at the end. In the UK, lenders may only offer this if you have a clearly understood and credible repayment strategy (FCA rule MCOB 11.6.41R).
Example: 400,000 home, 80,000 down, 6 %, 30 years
You borrow 320,000 (80 % loan-to-value).
| Repayment type | Monthly payment | Total interest |
|---|---|---|
| Repayment (fixed payment) | 1,918.56 | 370,683.35 |
| Equal principal | 2,488.89 falling to 892.93 | 288,799.66 |
| Interest-only | 1,600.00 + 320,000 at the end | 576,000.00 |
| Repayment + 2,400 extra per year | 1,918.56 | 281,216.73 (paid off after 23 years 9 months) |
In year one of the repayment mortgage, 19,093.10 goes to interest and only 3,929.62 to principal. An extra 200 a month (2,400 a year) cuts more than 89,000 of interest.
What is not included
This is principal and interest only. A US monthly housing payment usually also includes property tax and homeowners insurance, and a conventional loan with less than 20 % down may require private mortgage insurance (PMI) (CFPB). Arrangement fees, closing costs, stamp duty and rate changes are not included either. Check whether your lender charges an early repayment charge before making large overpayments.
Calculation rules as of 28 Sep 2026. This is a model calculation, not financial or tax advice. Your lender’s offer and amortization schedule are binding.
Frequently asked questions
How is a monthly mortgage payment calculated?
Payment = L · r · (1 + r)n ÷ ((1 + r)n − 1), with L = loan, r = annual rate ÷ 12 and n = months. For 320,000 at 6 % over 30 years (360 payments) that is 1,918.56 a month.
What is the payment on a 300,000 mortgage?
At 6 % it is 1,798.65 a month over 30 years and 2,531.57 over 15 years. At 3.5 % over 25 years it is 1,501.87. Enter your own rate to compare.
How much do extra payments save?
Every extra payment reduces the balance straight away, so all later interest falls. On 320,000 at 6 % over 30 years, 2,400 extra per year saves about 89,467 in interest and ends the loan 6 years 3 months early.
What is loan-to-value (LTV)?
LTV is the loan divided by the property value. 320,000 on a 400,000 home is 80 %. A lower LTV usually gets better rates; in the US, conventional loans with less than 20 % down may require PMI.
Repayment or interest-only mortgage?
A repayment mortgage is paid off by the end of the term. With interest-only the monthly payment is lower (1,600 instead of 1,918.56 in the example), but the full 320,000 is still owed at the end and total interest is much higher.
Does this include taxes and insurance?
No. The calculator shows principal and interest only, because property tax, insurance and PMI depend on where you live and on your policy. Add those amounts from your lender’s estimate to see the full monthly housing cost.
Sources and legal basis
- Consumer Financial Protection Bureau – What is amortization and how could it affect my loan?
- Consumer Financial Protection Bureau – What is private mortgage insurance (PMI)?
- MCOB 11.6.41R: FCA Handbook – interest-only mortgages need a credible repayment strategy
As of:
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