Your house payment depends on four things: the loan amount, the interest rate, the loan term, and whether you have property taxes and insurance rolled in
The core calculation is straightforward. If you borrow $300,000 at 6.5% interest over 30 years, your principal-and-interest payment is roughly $1,896 per month. But that number alone is not what you will actually pay. Most lenders require you to also pay property taxes, homeowners insurance, and possibly mortgage insurance, all bundled into one monthly bill called a PITI payment (principal, interest, taxes, insurance).
The principal-and-interest portion stays the same for the life of the loan. The taxes and insurance portions change — sometimes yearly, sometimes more often — so your total payment can shift even though your mortgage itself does not.
Key Takeaways
- Your principal-and-interest payment is locked in at signing and depends only on the loan amount, interest rate, and how many years you borrow for.
- Property taxes and homeowners insurance are added on top and can increase annually, raising your total monthly payment even if your mortgage rate does not change.
- Mortgage insurance (PMI) is required if you put down less than 20% and adds $100 to $300+ per month depending on the loan size and your down payment.
- You can estimate your payment using the loan amount, rate, and term, but your lender will give you the exact figure once they know the property taxes and insurance costs for your specific home.
How the principal-and-interest portion is calculated
Lenders use a fixed formula to turn a loan amount, interest rate, and term into a monthly payment. The formula accounts for the fact that early payments are mostly interest and later payments are mostly principal. A $300,000 loan at 6.5% over 30 years produces a $1,896 principal-and-interest payment. The same loan at 5.5% produces $1,703. The same loan at 7.5% produces $2,098.
The term matters just as much. A $300,000 loan at 6.5% over 15 years costs $2,896 per month in principal and interest — much higher, because you are paying it back in half the time. Over 20 years, it is $2,329. The longer the term, the lower the monthly payment, but the more total interest you pay over the life of the loan.
You can calculate this yourself using an online mortgage calculator (search "mortgage payment calculator"), or ask your lender for an estimate once you have a rate quote. The lender's number will be exact; a calculator gives you a close approximation.
Property taxes and insurance that get added to your payment
Your lender will require you to pay property taxes and homeowners insurance as part of your monthly mortgage payment. These are held in an escrow account — money set aside by the lender and paid to the taxing authority and insurance company on your behalf when they are due.
Property taxes vary wildly by location. A home worth $400,000 might have annual taxes of $4,000 in one county and $8,000 in another. Your real estate agent or the county assessor's office can tell you the tax rate for a specific property. Divide the annual tax by 12 to get the monthly amount added to your payment.
Homeowners insurance typically costs $800 to $2,000 per year depending on the home's value, location, age, and your coverage choices. Get quotes from at least two insurers before you lock in a rate. The lender will require proof of insurance before closing.
Mortgage insurance if your down payment is under 20%
If you put down less than 20%, your lender will require private mortgage insurance (PMI). This protects the lender if you stop paying, and it is added to your monthly bill.
PMI typically costs 0.5% to 1.5% of the loan amount per year, paid monthly. On a $300,000 loan, that is $125 to $375 per month. The exact rate depends on your credit score, the size of your down payment, and the lender's rules. A 10% down payment costs more in PMI than a 15% down payment on the same loan.
PMI can be removed once you reach 20% equity in the home — either by paying down the principal or by the home appreciating in value. Some lenders will remove it automatically once you hit that threshold; others require you to request it. Ask your lender about their PMI removal policy before you sign.
What your total monthly payment actually looks like
Here is a concrete example. You buy a $400,000 home with a $80,000 down payment (20%), so you borrow $320,000 at 6.5% over 30 years.
- Principal and interest: $2,023
- Property taxes (at 1% annually): $333
- Homeowners insurance: $125
- PMI: $0 (you put down 20%, so none required)
- Total monthly payment: $2,481
Now change one thing: you put down only $60,000 (15%), so you borrow $340,000 at the same rate and term.
- Principal and interest: $2,154
- Property taxes: $333
- Homeowners insurance: $125
- PMI: $255
- Total monthly payment: $2,867
The second scenario costs $386 more per month — not because the interest rate changed, but because you borrowed more and have to pay PMI. This is why down payment size matters so much to your monthly cost.
How interest rates move your payment up or down
Interest rates change daily based on market conditions. A rate that is available today may not be available next week. Even a 0.5% difference in rate produces a noticeable change in your monthly payment.
| Interest Rate | $300,000 Loan, 30 Years | Monthly Difference |
|---|---|---|
| 5.5% | $1,703 | — |
| 6.0% | $1,799 | +$96 |
| 6.5% | $1,896 | +$97 |
| 7.0% | $1,996 | +$100 |
| 7.5% | $2,098 | +$102 |
When you get a rate quote from a lender, ask how long it is locked in. Most lenders lock a rate for 30 to 60 days. If rates rise before you close, you may be able to lock a new rate, but you may also face a fee. If rates fall, you can sometimes renegotiate, depending on the lender's terms.
Getting an accurate estimate from your lender
Once you have a specific property under contract, a rate quote, and a down payment amount, your lender can give you a detailed estimate called a Loan Estimate. This document shows your principal-and-interest payment, the estimated property taxes and insurance, PMI if applicable, and all closing costs.
The Loan Estimate is required by federal law and must be provided within three business days of your application. It is not a final bill — property taxes and insurance may shift slightly before closing — but it is accurate enough to use for budgeting.
Do not rely on a calculator alone. Calculators are useful for rough comparisons, but your lender's Loan Estimate is the number you should use to decide whether you can afford the home.
Frequently Asked Questions
Can I pay off my mortgage faster by paying extra each month?
Yes. Any extra payment you make goes directly to principal, shortening the loan term and reducing total interest paid. Some lenders charge a prepayment penalty, so check your loan documents before you start. Most mortgages have no penalty.
What happens to my payment if interest rates drop after I lock in my rate?
Your payment stays the same — you are locked into the rate you agreed to. You can refinance to a lower rate later, but that involves closing costs and a new application. Refinancing makes sense only if the new rate is low enough to offset those costs over the time you plan to stay in the home.
Does my credit score affect my monthly payment?
Your credit score does not change the principal-and-interest payment itself, but it affects the interest rate you are offered. A higher score usually gets you a lower rate. It also affects the cost of PMI if you put down less than 20%.
What if my property taxes or insurance go up after I buy?
Your lender will adjust your escrow account and raise your monthly payment to cover the increase. You will receive notice of the change before it takes effect. This is why your actual payment can rise even though your mortgage rate does not.
Is there a way to avoid PMI if I cannot put down 20%?
Some lenders offer piggyback loans — a first mortgage for 80% of the home price and a second mortgage for part of the down payment, with no PMI on the first. This costs more in total interest but avoids PMI. Compare the total cost of both options before deciding.