Mortgage Calculator

What this Mortgage Calculator does

It estimates your full monthly housing payment — not just principal and interest, but the complete PITI (Principal, Interest, property Tax, and Insurance) that shows up on a real mortgage bill, plus PMI (private mortgage insurance) if your down payment is below 20% and HOA dues if the home has them. Choose between the two dominant US mortgage products — a 30-year fixed or 15-year fixed rate — or model a 5/1 or 7/1 ARM (adjustable-rate mortgage) and see how the payment could change after the initial rate period ends.

The formula behind the payment

Principal and interest use the standard fully-amortizing loan formula — equal payments for the whole term, with the interest/principal split shifting over time:

Where L is the loan amount (home price minus down payment), i is the monthly interest rate, and n is the number of monthly payments. Property tax is estimated as your entered rate applied to the home price, divided by 12; homeowners insurance is your annual estimate divided by 12; and PMI, when it applies, is your entered annual PMI rate applied to the loan balance, divided by 12. Adding all of those together gives the full PITI payment.

A worked example

A $410,700 home (the 2026 US median sale price) with 20% down ($82,140) leaves a $328,560 loan. On a 30-year fixed at 6.58%, principal and interest come out to about $2,094/month. Add roughly $339/month in estimated property tax (at the 0.99% national average rate) and $150/month in estimated insurance, and the full PITI payment lands around $2,583/month— about 23% more than the principal-and-interest figure alone. At exactly 20% down, PMI doesn't apply here; drop to 10% down on the same home and PMI alone would add roughly $231/month at a 0.75% PMI rate, on top of a larger loan balance.

Common mistakes when comparing mortgages

• Budgeting only for principal and interest: property tax, insurance, PMI, and HOA dues can easily add 20-30% (or more, in high-tax areas) on top of the loan payment itself.
• Not shopping the 15-year option: it usually carries a meaningfully lower rate than the 30-year, and the total interest savings over the life of the loan can be substantial — worth checking even if you expect to end up choosing the 30-year for payment flexibility.
• Underestimating an ARM's reset risk: a lower initial rate is real savings for the first several years, but budget for the payment to potentially rise (not just fall) once it adjusts — don't assume rates will stay where they are today.
• Forgetting closing costs: this calculator estimates the ongoing monthly payment, not the cash you need at the closing table — see the Down Payment / Affordability calculator for that side of the math.

Frequently asked questions

What actually moves this number

Specific levers, and roughly what each one is worth. Not “save more” — the things that change the figure above by an amount you can measure.

• Get quotes from several lenders on the same day

  Lender margin is a genuine spread on identical borrowers, and rate-shopping inquiries inside a 14-to-45-day window count as one for scoring. A quarter point on a $400,000 30-year loan is about $60/month and roughly $21,000 over the term, for an afternoon of phone calls.

• Check whether you are just below an LTV pricing band

  Pricing adjustments step at loan-to-value thresholds, so finding another 1-2% of down payment can drop your rate rather than just your balance. Ask the lender where the next band sits before you finalize the down payment — it is a question they will answer directly.

• Price the property tax for the specific parcel, not the state

  State averages run from about 0.27% to 2.11% of value, and counties inside one state can differ by more than a point. On a $400,000 home that is $90 to $703 a month. Pull the actual bill from the county assessor before deciding what you can afford.

• Ask what the rate is without points

  A quoted rate frequently includes discount points you did not ask for. Divide the point cost by the monthly saving to get the break-even in months, then compare it honestly to how long you expect to keep the loan — most people do not keep a 30-year mortgage for 30 years.

What this calculator does not cover

Every calculator simplifies, and the useful thing is knowing exactly where. These are the specific gaps between this estimate and your real situation:

• Property tax uses a state average. Rates are set by county, city, and school district, and can vary by more than a full percentage point between neighboring jurisdictions within one state.
• Homeowners insurance is an estimate, not a quote. Premiums vary sharply by region, construction, claims history, and have risen steeply in some markets.
• It models principal, interest, taxes, and insurance. It does not include HOA dues, maintenance, or utilities, which together often add several hundred dollars a month to the real cost of owning.
• Closing costs are not part of the monthly payment and are not included here — budget 2% to 5% of the purchase price separately.
• The default interest rate is a survey average from a specific week, not a quote for you. Your actual rate depends on credit score, loan-to-value, property type, and occupancy.

For anything that turns on an exact figure, use the primary sources below or a qualified professional. How these limits are decided and disclosed is described in the editorial standards.