How to Calculate Mortgage Payment: The Formula, Examples, and PITI Breakdown

TL;DR: Your monthly mortgage payment has four parts: principal, interest, taxes, and insurance (PITI). The core formula is M = P[r(1+r)^n]/[(1+r)^n-1], where P is the loan amount, r is the monthly interest rate, and n is the number of payments. A $300,000 loan at 6.5% over 30 years costs roughly $2,017 per month before taxes and insurance.

You have seen the listing. You have played with the numbers on Zillow. And somewhere between the asking price and your bank account, a question keeps bouncing around: what will my actual monthly payment be?

Most people assume the mortgage payment is just principal and interest. That is the number lenders advertise, the number on the amortization schedule, and the number that looks manageable. But your real payment is bigger than that. Property taxes, homeowners insurance, and potentially private mortgage insurance all stack on top of the principal and interest, and in some markets they add $500 to $1,000 or more to what you pay each month.

This guide walks through exactly how to calculate mortgage payment using the standard formula, how interest rates and loan terms change the number, and how to build a full PITI estimate so you know what you are actually signing up for. By the end, you will be able to calculate your payment by hand and know where the hidden costs hide.

What Is a Mortgage Payment and What Does It Include?

A mortgage payment is the fixed amount you pay each month to repay your home loan. But the payment itself is a bundle of four distinct costs, and understanding each one matters because they behave differently over time.

The Four Components of PITI

PITI mortgage payment explained: your monthly payment is made up of four pieces:

Some borrowers also pay private mortgage insurance (PMI) if their down payment is less than 20%, and HOA fees if they buy in a homeowners association community. These are not technically part of PITI, but they are part of your real monthly housing cost.

The principal and interest portion is what the standard mortgage formula calculates. Taxes, insurance, PMI, and HOA fees are added on top. That is why two borrowers with the same loan amount and interest rate can have very different monthly payments, one might pay $2,400 total while the other pays $3,100 because of higher property taxes, a PMI requirement, or HOA dues.

How to Calculate Your Monthly Mortgage Payment

The standard way to calculate a mortgage payment uses the amortization formula. It looks intimidating at first, but it breaks down into three simple inputs.

The Standard Amortization Formula

Mortgage payment formula:

M = P × [r(1 + r)^n] / [(1 + r)^n - 1]

Where:

• M = your monthly payment
• P = the loan principal (home price minus down payment)
• r = the monthly interest rate (annual rate divided by 12)
• n = the total number of payments (loan term in years multiplied by 12)

That is the entire formula. Three inputs, one calculation. No guessing, no online tools required, though using one saves time and reduces errors.

Worked Example 1: $300,000 Loan at 6.5% Over 30 Years

Let us walk through a real scenario. You buy a $350,000 home with a 10% down payment of $35,000. Your loan amount is $315,000. The interest rate is 6.5% on a 30-year fixed.

Inputs:

• P = $315,000
• r = 6.5% / 12 = 0.005417
• n = 30 × 12 = 360

Calculation:

• (1 + r)^n = (1.005417)^360 = 6.9916
• r × (1 + r)^n = 0.005417 × 6.9916 = 0.03788
• (1 + r)^n - 1 = 5.9916
• M = $315,000 × (0.03788 / 5.9916) = $315,000 × 0.006323 = $1,992

Your monthly principal and interest payment is roughly $1,992. That is the number the formula gives you. Now add the other costs to find your real payment.

Worked Example 2: $400,000 Loan at 7% Over 30 Years

Say you are buying a more expensive home. $500,000 purchase price, 20% down payment of $100,000, loan amount of $400,000 at 7% over 30 years.

Inputs:

• P = $400,000
• r = 7% / 12 = 0.005833
• n = 360

Calculation:

• (1 + r)^n = (1.005833)^360 = 8.1165
• r × (1 + r)^n = 0.005833 × 8.1165 = 0.04735
• (1 + r)^n - 1 = 7.1165
• M = $400,000 × (0.04735 / 7.1165) = $400,000 × 0.006654 = $2,662

Principal and interest alone is $2,662 per month. Before taxes, insurance, or anything else.

How Interest Rate Affects Your Payment

The interest rate is the single biggest lever on your monthly payment. A half-point change on a $300,000 loan adds or removes roughly $100 per month. Over 30 years, that half-point costs or saves you roughly $36,000.

Here is what different rates look like on the same $300,000 loan over 30 years:

At 5%, your total interest over 30 years is $279,768. At 7.5%, it is $455,279. Same loan amount, same 30-year term, $175,511 difference in total cost. That is why shopping for the best mortgage rate matters so much, and why even a small improvement in your credit score before applying can pay for itself many times over.

How a 0.25% Rate Drop Changes the Math

If you are deciding whether to buy points at closing or wait for a slightly lower rate, here is the comparison on a $300,000 loan:

One point saves $49 per month and costs $3,000. You break even at month 61, roughly 5 years. If you plan to stay in the home longer than that, buying the point pays off. If you might move or refinance in 3 to 5 years, skip it.

How Loan Term Changes the Math

The loan term, how many years you take to repay the loan, is the second-biggest factor in your monthly payment. A shorter term means higher monthly payments but dramatically less total interest.

15-Year vs 30-Year Mortgage Comparison

Here is a side-by-side on a $300,000 loan at 6.5%:

The 15-year term saves $212,430 in interest, but costs $717 more per month. That is a significant jump. The right choice depends on whether your budget can handle the higher payment without stretching too thin.

15 year vs 30 year mortgage calculator thinking: if you can comfortably afford the 15-year payment and still have room for savings, emergencies, and life, the 15-year term is the better financial move. But if the 15-year payment pushes your total housing cost above 35% to 40% of your gross income, take the 30-year and make extra principal payments when you can. The flexibility of the lower required payment is worth more than the interest savings if it keeps you from becoming house-poor.

Adding Taxes, Insurance, and PMI to Get Your Real Payment

The formula gives you principal and interest. Your real monthly housing cost includes property taxes, homeowners insurance, and potentially PMI. Here is how to build the full picture.

Full PITI Example

Using the $315,000 loan from earlier at 6.5% over 30 years:

The principal and interest is $1,992. The full payment is $2,569. That is a $577 difference, roughly 29% more than the P&I number alone. And that is before any HOA fees.

How Property Taxes Change by State

Property taxes vary enormously. Here are effective rates for a few states on a $350,000 home:

A buyer in Texas pays $467 per month in property taxes on the same home that costs $93 per month in Hawaii. That is a $374 monthly difference on a $350,000 home, just from property taxes. If you are shopping across state lines, using a property tax calculator by state before making an offer prevents payment shock.

When PMI Applies and How to Remove It

PMI mortgage insurance explained: if your down payment is less than 20% on a conventional loan, lenders require private mortgage insurance to protect them against default. PMI typically costs 0.3% to 1.5% of the loan amount per year, depending on your credit score and down payment size.

On a $315,000 loan, a 0.5% PMI rate adds $131 per month. The good news is that PMI is temporary. Once you reach 20% equity, either through payments or home appreciation, you can request PMI removal. At 22% equity, your lender must automatically cancel it.

How to avoid PMI without 20% down: some borrowers use an 80/10/10 structure, an 80% first mortgage, 10% second mortgage or HELOC, and 10% down payment. Others use lender-paid PMI in exchange for a slightly higher rate. Each approach has trade-offs. See our guide to what is PMI for the full breakdown.

How to Calculate Mortgage Payment by Hand: A Step-by-Step Guide

If you want to verify what a calculator is telling you, or if you just want to understand the math, here is the process broken into steps.

Step 1: Convert your annual interest rate to a monthly rate. Divide by 12. A 6.5% annual rate becomes 0.065 / 12 = 0.005417.

Step 2: Calculate the number of total payments. Multiply the loan term in years by 12. A 30-year loan has 360 payments. A 15-year loan has 180.

Step 3: Raise (1 + monthly rate) to the power of total payments. Using our example: (1.005417)^360 = 6.9916.

Step 4: Multiply the monthly rate by that result. 0.005417 × 6.9916 = 0.03788.

Step 5: Subtract 1 from the result in Step 3. 6.9916 - 1 = 5.9916.

Step 6: Divide the result in Step 4 by the result in Step 5. 0.03788 / 5.9916 = 0.006323.

Step 7: Multiply by the loan principal. $315,000 × 0.006323 = $1,992.

That is your monthly principal and interest payment. Add property taxes, insurance, and PMI to get your full monthly housing cost.

Quick Reference: Payment Per $100,000 Borrowed

If you do not want to run the full formula every time, here are pre-calculated P&I payments per $100,000 borrowed:

Multiply the table value by your loan amount in hundreds of thousands. A $300,000 loan at 6.5% over 30 years is 3 × $632 = $1,896. Quick, dirty, and accurate enough for initial budgeting.

Common Mistakes When Calculating Mortgage Payments

Forgetting that P&I is not the full payment. The formula gives you two of the four components. Taxes, insurance, and PMI can add 25% to 40% to your monthly cost. Always calculate PITI, not just P&I.

Using the wrong interest rate. Your interest rate is not the same as the APR. The APR includes closing costs and fees spread over the loan term. For payment calculations, use the stated interest rate, not the APR.

Ignoring property tax differences. A home in Texas and a home in Colorado at the same price have wildly different monthly payments because of property taxes. If you are comparing homes across state or county lines, factor in the local tax rate before you decide what you can afford.

Not accounting for PMI. If you are putting less than 20% down on a conventional loan, PMI adds $100 to $250 or more per month depending on your loan amount and credit score. FHA loans have their own mortgage insurance premium (MIP) that works differently. See our US loan programs guide for the differences.

Assuming your payment stays flat. Property taxes get reassessed. Insurance premiums go up. If your payment is based on an escrow account, expect it to increase over time. Budget a 10% to 15% buffer above your initial estimate.

The Bottom Line

How to calculate mortgage payment comes down to understanding the formula, knowing your inputs, and adding the costs that the formula does not include. Principal and interest is the starting point. Property taxes, homeowners insurance, and PMI are the reality check.

Use the standard amortization formula or the US Mortgage Calculator to find your P&I. Then layer on taxes, insurance, and PMI to find your real monthly cost. The difference between the two numbers is where most first-time buyers get surprised.

Run your numbers before you fall in love with a listing. A few minutes of math now saves you from years of payment shock.

Frequently Asked Questions

This article is for educational and informational purposes only and does not constitute financial, mortgage, or legal advice. Mortgage payment calculations are estimates based on the standard amortization formula and typical market data. Actual payments vary by lender, loan program, interest rate, property taxes, insurance premiums, and other factors. Always verify your specific numbers with a licensed mortgage professional or lender before making financial decisions.