Mortgage Calculator

Intro

Use this mortgage calculator to estimate the monthly principal and interest repayment on a home loan. Enter the property price, deposit (down payment), interest rate, and term to see the approximate payment before comparing lender quotes.

What this mortgage calculator does

The calculator subtracts your deposit from the property price to estimate the loan amount. It then spreads that loan across the term using a standard repayment mortgage formula.

It is best for quick planning questions such as:

• How much might the monthly payment be on a given property price?
• How does a larger deposit change the repayment?
• What happens if the interest rate or term changes?
• How much borrowing is left after the deposit?

How it works

The calculation assumes a fixed interest rate and equal monthly repayments. Each payment includes interest for the month and a repayment of part of the loan balance.

The monthly repayment formula is P * r(1+r)^n / ((1+r)^n - 1). In this formula, P is the loan amount, r is the monthly interest rate, and n is the total number of monthly payments.

At zero interest, the calculator divides the loan amount evenly across the number of months. For background on how payments reduce the balance, see the CFPB’s explanation of amortization.

Example calculation

The worked examples on this page use US dollars (USD). Choosing UK - GBP changes the calculator's currency labels; it does not convert your entries or these examples.

Enter a property price of $300,000, a deposit of $60,000, an annual interest rate of 5.5%, and a mortgage term of 30 years. The starting loan is $300,000 - $60,000 = $240,000, repaid over 30 × 12 = 360 months.

With r = 0.055 / 12:

Monthly payment = 240,000 × r / (1 - (1 + r)^(-360)) = $1,362.69

The first month’s interest is $240,000 × 0.055 / 12 = $1,100.00. About $262.69 of the payment reduces the balance, leaving $239,737.31. Later payments contain less interest as the loan falls.

Totals use the unrounded payment, about $1,362.693603, rather than multiplying the displayed rounded figure by 360. The total mortgage repayments exclude the $60,000 deposit and all other purchase and ownership costs.

At 0% interest, the same $240,000 loan over 360 months would be $666.67 per month, rounded from $240,000 / 360.

How to use the result

Use the result to plan principal-and-interest payments. It does not assess affordability or provide a lender offer. A real mortgage quote may include arrangement fees, valuation fees, mortgage insurance, product fees, taxes, service charges, homeowners insurance, or local property costs.

For a more cautious estimate, try a higher interest rate and a shorter term. For a deposit plan, compare this page with the Savings Goal Calculator.

Assumptions and limitations

• This is a repayment mortgage with principal and interest paid monthly. It does not model an interest-only loan, balloon payment, offset account or overpayments.
• The annual percentage is divided by 12 and stays fixed for the full term. A rate fixed for only an introductory period is not a forecast for the entire mortgage.
• Property taxes, insurance (including homeowners insurance and private mortgage insurance, PMI), maintenance, service charges, purchase taxes, fees and early repayment charges are excluded.
• Monthly interest and full-precision payments may differ from a lender’s daily interest, payment dates and cent-rounding rules.
• The property price must exceed the deposit, the term must be positive and the rate cannot be negative. A deposit covering the entire price needs no mortgage, but is outside this calculator’s borrowing inputs.
• It does not assess eligibility, income, credit history or lender affordability rules. This is an educational estimate, not an offer or financial advice.
• Use one currency consistently; changing the currency display does not convert the property price or deposit.

How we explain formulas, assumptions and sources