To calculate a fixed-rate mortgage’s scheduled monthly principal-and-interest payment, use the loan amount, monthly interest rate, and number of payments. That figure is not the full monthly cost of owning the home, and it is not the same as the loan’s total borrowing cost. For a U.S. mortgage, calculate and compare each measure separately.
How do mortgage lenders calculate monthly payments?
For a fixed-rate, fully amortizing loan with monthly payments, the principal-and-interest (P&I) payment is calculated with this formula:
M = P × r(1 + r)n ÷ ((1 + r)n − 1)
- M is the monthly P&I payment.
- P is the amount borrowed, not the home’s purchase price. Subtract the down payment from the price, then account for any costs rolled into the loan.
- r is the monthly interest rate. Convert the annual rate to a decimal and divide by 12; for example, 4% becomes 0.04 ÷ 12.
- n is the number of monthly payments: the loan term in years multiplied by 12.
The Consumer Financial Protection Bureau (CFPB) says the payment depends on the loan amount, term, and interest rate. Its illustration of a $100,000 loan for 30 years at 4% gives a monthly P&I payment of $477. This is a rounded example, not a current rate quote or a personalized estimate. CFPB: How do mortgage lenders calculate monthly payments?
Check the full-term arithmetic
Multiply the scheduled monthly P&I payment by the number of scheduled payments to estimate total scheduled P&I. Subtract the original loan principal from that result to estimate scheduled interest. The final payment can vary because of rounding or servicing details, and paying off or refinancing early changes the schedule.
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How to estimate the monthly housing payment
Your monthly housing outlay may include more than P&I:
- Mortgage insurance, if applicable.
- Property taxes.
- Homeowners insurance.
- HOA dues and other applicable housing costs.
A lender’s monthly payment may combine P&I with mortgage insurance and escrow collections for taxes and homeowners insurance. If taxes or insurance are not escrowed, you still need to budget for them even though you pay them directly rather than sending them to the mortgage company. HOA dues are usually separate. Escrow amounts can change when tax or insurance bills change, even if fixed-rate P&I stays level. See the CFPB explanation of what is included in a monthly mortgage payment.
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Taxes and homeowners insurance are costs of owning the home, not interest or loan costs. On your Loan Estimate, check which expenses are not escrowed and whether the estimated total monthly payment fits your budget. Use current estimates from the relevant local tax authority and an insurance provider rather than assuming the lender’s figures are final. CFPB: Loan Estimate explainer
What does “total cost” mean for a mortgage?
There is no single “total cost” figure that answers every question. Identify the measure before you calculate or compare it.
| Measure | What it includes | How to interpret it |
|---|---|---|
| Total scheduled P&I | All scheduled principal and interest payments over the assumed term. | Multiply scheduled monthly P&I by the number of payments. It includes repayment of principal as well as interest. |
| Scheduled interest | Interest in those scheduled P&I payments. | Subtract the original principal from total scheduled P&I, subject to the actual schedule and loan terms. |
| Borrowing cost or finance charge | Interest and applicable loan charges over the assumed loan life, such as origination charges, discount points, and mortgage insurance. | Use the borrower’s disclosures rather than treating the P&I calculation as a complete borrowing-cost calculation. The Closing Disclosure shows the finance charge in its Loan Calculations section. |
| Closing Disclosure “Total of Payments” | Scheduled principal, interest, mortgage insurance if applicable, and loan costs, assuming payments are made as agreed through the loan’s end. | This is a disclosed total for the loan, not a monthly payment or a complete lifetime household budget. |
| Total housing expenditure | A household budget may also include property taxes, homeowners insurance, HOA fees, maintenance, utilities, and transaction expenses. | These are broader ownership expenses; do not assume they are all included in the lender’s “Total of Payments.” |
The CFPB’s explanation of “Total of Payments” describes the amount paid over the mortgage’s life under the stated assumptions. Your Closing Disclosure also lists APR and Total Interest Percentage (TIP) as separate calculations. APR helps compare loan costs and is not the same as the note interest rate; TIP expresses total interest as a percentage of the loan amount. Use the disclosures for the actual loan terms rather than trying to reproduce regulatory disclosure figures with the simple P&I formula. CFPB: What is the Total Interest Percentage?
How to compare mortgage offers
Compare Loan Estimates for the same loan amount, product, and term. Review both the ongoing payment and the upfront costs; a lower monthly payment alone does not establish that an offer is less expensive.
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- Note rate and whether it is fixed or adjustable.
- Monthly P&I, mortgage insurance, and estimated total monthly payment.
- Taxes, insurance, and other expenses not included in escrow.
- Origination charges, discount points, lender credits, and cash to close.
- APR and other disclosed cost measures.
- For an ARM, the rate-reset terms and a plausible higher-rate payment scenario; for a balloon loan, the due date and size of the final balance.
Rates can change daily, so estimates issued on different dates may reflect market timing as well as lender pricing. CFPB describes a five-year borrowing-cost comparison on the Loan Estimate: subtract the principal paid off in five years from the “In 5 years” amount, which includes principal, to estimate interest and fees paid over that period. For an ARM, that estimate assumes rates stay the same. The CFPB reports that borrowers keep a mortgage for about five years on average before moving or refinancing; that is contextual guidance, not a prediction for an individual borrower. CFPB: Compare Loan Estimates
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When the standard mortgage formula does not predict future payments
Adjustable-rate mortgages
The formula gives a level payment for a rate that remains unchanged. For an ARM, the CFPB says the initial payment is calculated as though the initial rate lasted for the full term. When the rate adjusts, the payment is typically recalculated using the new rate and remaining term. You can use the formula to estimate a payment period at a specified rate, but you cannot predict later payments without assumptions about future adjustments. CFPB mortgage-payment guidance
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Balloon loans
A balloon loan can have regular payments calculated over a longer period than the time before a large final balance is due. In the CFPB’s example, a $100,000 loan at 4% calculated over 30 years has $477 monthly P&I, but after five years of payments the balloon balance is $90,448. The figures are an illustration, not a quote. The example shows why a manageable regular payment does not by itself tell you the eventual payoff obligation or total cost. CFPB mortgage-payment guidance
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