Understanding Your Full Mortgage Payment

When most people think about a mortgage payment, they picture the loan itself: the principal you borrowed and the interest the bank charges. But the check you actually write each month usually covers four things, often called PITI: Principal, Interest, Taxes, and Insurance. If your down payment is below 20%, your lender will tack on private mortgage insurance (PMI), and if you're buying in a community with shared amenities, you'll also owe a homeowners association (HOA) fee. Our mortgage calculator includes all six pieces so the number you see is what you'll really pay, not a sticker price that surprises you at closing.

How the Math Works

The principal-and-interest portion of your payment uses the standard amortizing-loan formula:

Where P is the loan amount (home price minus down payment), r is your monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments (years × 12). The other pieces are simpler: property tax and home insurance are annual figures divided by 12, HOA is already monthly, and PMI is calculated as a small percentage of the loan balance divided by 12.

What matters here is that your interest is front-loaded. In the early years of a 30-year loan, the vast majority of each payment goes to interest, not principal, which is why the amortization schedule on this page is worth scrolling through. Switch it to "Monthly" view and look at how slowly the balance moves in year one versus year twenty-five.

A Worked Example

Say you're buying a $400,000 home with $80,000 down (20%) at a 6.75% interest rate on a 30-year loan, with $4,800/year in property tax and $1,800/year in home insurance. Here's how the math shakes out:

• Loan amount: $320,000
• Principal & interest: roughly $2,076/month
• Property tax: $400/month
• Home insurance: $150/month
• PMI: $0 (you're at 20% down, so it's waived)
• Total monthly payment: about $2,626

Drop the down payment to $40,000 (10%) and two things happen: your loan jumps to $360,000, and PMI of roughly $180/month gets added on top. Your monthly cost climbs by close to $400, even though you "saved" $40,000 up front. This is one of the biggest decisions in homebuying and our calculator lets you flip between scenarios in seconds.

Paying It Down Faster: Biweekly & Extra Payments

The "Pay It Down Faster" card on the calculator isn't a gimmick. Small changes have outsized effects because of how interest compounds. Two common strategies:

Biweekly payments. Instead of paying once a month (12 payments per year), you pay half your monthly amount every two weeks. Because there are 52 weeks in a year, that works out to 26 half-payments, or the equivalent of 13 full monthly payments instead of 12. On a 30-year mortgage, that one extra payment per year typically shaves about 5-7 years off the loan and saves tens of thousands in interest. Confirm with your lender that they apply biweekly payments to principal as they arrive, not just hold them until the end of the month.

Extra principal payments. Adding even $100-$200 a month to your payment goes straight to the principal, which means it's not earning the bank interest for the next 30 years. Run the calculator with and without an extra payment and look at the "Interest Saved" number. Most people are surprised.

Common Mistakes to Avoid

• Forgetting taxes and insurance. A "$1,800/month mortgage" advertised by a lender is usually just principal and interest. Real PITI is often 25-40% higher.
• Ignoring PMI. If you're putting less than 20% down, PMI is automatic and typically runs 0.3% to 1.5% of the loan per year. It eventually drops off, but only when your loan-to-value ratio hits 78-80%.
• Confusing interest rate with APR. APR includes fees and is what you should compare across lenders.
• Underestimating closing costs. Plan for 2-5% of the loan amount on top of your down payment.
• Choosing 30 years on autopilot. A 15-year loan has a higher monthly payment but cuts total interest by more than half. Worth running both terms in the calculator.

Frequently Asked Questions