The basic formula for a house payment

Your monthly house payment has four parts: principal, interest, property taxes, and homeowners insurance. The first two are built into your loan. The last two depend on where the house is and what it costs. Most people use the acronym PITI to mean all four together.

The principal and interest portion stays the same every month if you have a fixed-rate mortgage. Property taxes and insurance can shift year to year. If you have an escrow account—which most lenders require—your lender collects a portion of taxes and insurance each month and pays them on your behalf when they're due.

To estimate your payment, you need three numbers: the loan amount, the interest rate, and the loan term in years. From there, you can calculate principal and interest by hand or use an online calculator. Then you add estimated property taxes and insurance.

Key Takeaways

  • Principal and interest are calculated from your loan amount, interest rate, and how many years you'll pay—these two stay the same every month on a fixed-rate mortgage.
  • Property taxes vary by county and city, so you need to research the tax rate for the specific house or neighborhood you're looking at.
  • Homeowners insurance quotes come from insurance companies directly, and you should get at least two quotes before estimating your total payment.
  • If you're putting down less than 20 percent, add mortgage insurance (PMI) to your estimate, which typically costs 0.5 to 1.5 percent of the loan amount per year.
  • Online mortgage calculators can do the math for you, but you still need to input accurate numbers for taxes and insurance to get a realistic total.

Calculating principal and interest

The formula for monthly principal and interest is: M = P [ r(1 + r)^n ] / [ (1 + r)^n – 1 ]. In plain terms: M is your monthly payment, P is the loan amount, r is the monthly interest rate (annual rate divided by 12), and n is the total number of payments (years times 12).

If you borrowed $300,000 at 6.5 percent interest over 30 years, your monthly principal and interest would be roughly $1,896. If the same loan was for 15 years instead, it would be about $2,596 per month—higher because you're paying it back faster.

You do not have to do this math by hand. Mortgage calculators on Bankrate, NerdWallet, and most lender websites will compute this for you. Enter the loan amount, rate, and term, and the calculator shows your principal and interest in seconds. The result is always the same regardless of which calculator you use, because the math is standardized.

Finding property tax estimates

Property taxes are set by your county or municipality and are based on the assessed value of the house, not the purchase price. A house that sells for $400,000 might be assessed at $350,000 or $420,000 depending on local rules and recent sales data in the area.

To estimate taxes, find the property tax rate for the county where the house is located. Most county assessor websites publish this rate as a percentage or as a dollar amount per $1,000 of assessed value. If the rate is 1.2 percent and the assessed value is $350,000, your annual tax would be $4,200, or $350 per month.

Tax rates vary widely. New Jersey and Illinois have rates above 2 percent in many counties. Hawaii and Alabama have rates below 0.5 percent. If you're comparing houses in different areas, property taxes can swing your total payment by hundreds of dollars per month.

Getting homeowners insurance quotes

Homeowners insurance protects the lender's investment in the house. Lenders require it before they will fund a loan. The cost depends on the house's age, condition, location, and the coverage limits you choose.

Contact at least two insurance companies directly—State Farm, Allstate, GEICO, and local independent agents all write homeowners policies. Give them the same house details and ask for a quote on the same coverage level. Quotes for the same house can differ by $500 or more per year between companies.

A typical homeowners insurance policy for a $300,000 house in a moderate-risk area costs between $1,000 and $1,500 per year, or $83 to $125 per month. Older homes, homes in flood zones, or homes in areas with high theft rates cost more. Once you have two or three quotes, use the middle estimate in your payment calculation.

Accounting for mortgage insurance if you put down less than 20 percent

Mortgage insurance (PMI) protects the lender if you default. If your down payment is less than 20 percent of the purchase price, your lender will require it. PMI typically costs between 0.5 and 1.5 percent of the loan amount per year, depending on your credit score and how much you're putting down.

If you borrowed $240,000 (putting 20 percent down on a $300,000 house) at 6.5 percent, PMI might cost $1,200 to $3,600 per year, or $100 to $300 per month. This is added to your principal and interest payment. PMI drops off automatically once you reach 20 percent equity in the home, which usually takes 5 to 10 years depending on how fast home values rise and how much extra you pay toward principal.

Putting the pieces together

Once you have all four numbers, add them: principal and interest + property taxes + homeowners insurance + PMI (if applicable) = your estimated total monthly payment.

A realistic example: $300,000 house, 10 percent down ($30,000), 6.5 percent interest, 30-year loan. Principal and interest: $1,896. Property taxes (1.2 percent rate, $330,000 assessed): $330 per month. Homeowners insurance: $100 per month. PMI (0.8 percent): $216 per month. Total: $2,542 per month.

This is what you owe the lender and the escrow account each month. It does not include utilities, maintenance, HOA fees (if applicable), or other costs of owning a home. Those are separate expenses you should budget for.

Why your actual payment might differ from your estimate

Property tax assessments are reassessed every few years in most places. If your house is reassessed upward, your tax bill and escrow payment will increase. Insurance companies also raise rates periodically, especially after claims or in areas where claims are rising.

Interest rates change daily. If you lock in a rate with a lender, that rate is good for a set period—usually 30 to 60 days. If you do not close within that window, you may be offered a different rate. Shop around and compare locked rates from multiple lenders before you commit.

Some lenders charge origination fees, appraisal fees, or title insurance fees that are rolled into your loan. These do not change your monthly payment but do increase the total amount you borrow. Ask your lender for a Loan Estimate, which shows all fees and your final loan amount before you sign anything.

Frequently Asked Questions

What is the difference between a fixed-rate and adjustable-rate mortgage?

A fixed-rate mortgage keeps the same interest rate for the entire loan term, so your principal and interest payment never changes. An adjustable-rate mortgage (ARM) has a lower rate for the first few years, then adjusts up or down based on market conditions. ARMs are riskier because your payment can jump significantly after the initial period. For estimation purposes, assume a fixed rate unless you are specifically considering an ARM.

Do I need to include HOA fees in my house payment estimate?

HOA fees are separate from your mortgage payment. They go to the homeowners association, not your lender. If the house has an HOA, ask the seller or real estate agent for the monthly fee amount and add it to your total housing costs, but it is not part of PITI.

Can I pay off my mortgage faster than the loan term?

Yes. You can make extra payments toward principal at any time without penalty on most mortgages. Paying extra reduces the total interest you pay and shortens the loan term. However, your required monthly payment stays the same unless you refinance. Extra payments are optional, not required.

What happens to my escrow account if I pay off my house early?

When you pay off the loan, the lender releases any remaining escrow balance to you, usually within 30 to 45 days. You then become responsible for paying property taxes and insurance directly to the county and insurance company instead of through the lender.

How accurate are online mortgage calculators?

Online calculators are accurate for principal and interest if you input the correct loan amount, rate, and term. They are only as accurate as the property tax and insurance numbers you enter. If you use estimated or outdated figures for taxes and insurance, your total will be off. Use current quotes and tax rates from the specific county for the best estimate.