How to Calculate a Mortgage Payment
A practical walkthrough of fixed-rate mortgage payments, interest, and housing costs.
A mortgage payment has more than one component. For a standard fixed-rate fully amortizing home loan, the principal-and-interest portion is determined by the amount borrowed, monthly interest rate, and number of scheduled payments. Property tax, insurance, and other housing expenses are generally separate.
Mortgage principal and monthly interest
Start with the purchase price and subtract your down payment to get the loan principal. Convert the stated annual interest rate to a monthly rate by dividing by 12 when the lender uses that convention. Finally, multiply the loan term in years by 12 to determine the number of payments.
For example, a $300,000 property with a $60,000 down payment has a $240,000 loan principal. At 6% nominal annual interest for 30 years, the monthly rate is 0.005 and there are 360 scheduled monthly payments.
Fixed-rate payment formula
For principal P, monthly rate r, and number of payments n, the monthly principal-and-interest amount is:
M = P × r × (1 + r)^n ÷ [(1 + r)^n − 1]
At a zero interest rate, use M = P ÷ n. Applying the formula to the example above produces a payment of approximately $1,438.92 before taxes, insurance, or fees.
Why early payments contain more interest
Interest each month is based on the outstanding loan balance. For the first month of this example, interest is approximately $1,200 ($240,000 × 0.005). The remainder of the $1,438.92 payment, about $238.92, reduces principal. As principal falls, the interest portion generally declines while more of the fixed payment pays down the balance.
Estimate the full monthly housing cost
A mortgage calculator may let you enter property taxes, homeowners insurance, association charges, or mortgage insurance. These costs can change independently of the loan’s fixed principal-and-interest payment. A quoted rate also may not capture every lender fee; review the loan’s APR and disclosures separately.
Compare scenarios responsibly
Run the calculator with several down payments, interest rates, and terms. A shorter term commonly produces a higher required payment but lower total interest, all else equal. Do not compare only the monthly payment: review upfront costs, prepayment conditions, total interest, and affordability.
Common questions
Does the calculator include property tax? Only if you supply it as an added cost in a calculator that supports that input.
Does extra payment save interest? Typically yes when the lender applies the extra amount to principal without offsetting penalties.
Is the result an official loan quote? No. Mortgage quotations depend on the lender, credit profile, property, and local rules.