How this mortgage calculator works
The estimate combines a fixed-rate loan payment with the recurring housing costs you enter. The loan amount is the home price minus your down payment. The principal-and-interest portion pays down that loan over equal monthly installments.
Annual property taxes and homeowners insurance are divided by twelve. Monthly HOA dues and any PMI estimate you enter are then added. Those costs may be paid through escrow or separately; either way, they affect your monthly budget.
The payment formula
For a positive interest rate, the monthly principal-and-interest payment is:
M = P × r / (1 − (1 + r)^(−n))
- P is the original loan principal.
- r is the annual interest rate divided by 100 and then by 12.
- n is the number of years multiplied by 12.
- M is the monthly principal-and-interest payment.
At zero interest, the formula is M = P / n. If the home is fully paid for, the loan payment and PMI are zero; the other housing costs remain. We keep precision during calculation, round each monthly cost to cents, then add those rounded costs to get the displayed total. A lender may use different rounding or payment timing.
A worked example
For a $400,000 home with 20% down ($80,000), the loan is $320,000. At 6% annual interest over 30 years, the monthly rate is 0.005 and there are 360 payments.
The formula gives $1,918.56 in monthly principal and interest. Add $400.00 for $4,800 in annual property taxes and $150.00 for $1,800 in annual insurance. With no HOA dues or PMI entered, the total is $2,468.56 per month. These are illustrative inputs, not current market rates or typical costs for a particular area.
What the result means
Use the breakdown to distinguish the loan payment from other ownership costs. A loan with a manageable principal-and-interest payment can still leave little room for other spending after taxes, insurance and upkeep.
This is a payment estimate, not an affordability assessment. It does not consider income, other debts, emergency savings or future expenses. Closing costs, maintenance, utilities, flood insurance and special assessments are excluded. Revisit tax and insurance estimates as you learn more about the property.
Frequently asked questions
Does the payment include taxes and insurance?
Yes, if you enter them. The result includes one twelfth of each annual estimate. The calculator does not look up local tax rates or insurance quotes.
How should I enter PMI?
Choose a monthly amount or an annual percentage of the original loan principal, using an estimate from your lender. “Not included” contributes zero. We do not decide whether you need PMI, model cancellation, or estimate FHA or other government-program mortgage insurance.
Should I use the interest rate or APR?
Use the loan’s stated interest rate. APR incorporates additional borrowing costs and is not the rate used in this scheduled-payment formula.
Will my payment stay the same?
The principal-and-interest portion is fixed under these assumptions. Taxes, insurance, HOA dues and mortgage insurance may change. Adjustable rates, balloon payments and interest-only periods are outside this model.
Are my financial inputs saved?
We do not save them. Values are held in this page’s browser memory; your browser may restore the page when navigating back. We do not send inputs or calculated results to analytics. See our privacy page for information about general usage analytics.
Sources & review
- Mortgage interest rate versus APR — Consumer Financial Protection Bureau
- Principal and interest versus total monthly payment — Consumer Financial Protection Bureau
- What is PITI? — Consumer Financial Protection Bureau
- What is private mortgage insurance? — Consumer Financial Protection Bureau
Last reviewed: . The formula is reproduced above so you can check the math independently.
For informational estimates only. This tool is not a loan quote, approval, or individualized financial, tax or legal advice. Confirm rates, insurance, taxes and terms with the relevant providers.