How to Calculate Your Monthly Mortgage Payment (With Real Examples)

How to Calculate Mortgage Payment: The Formula Explained

Understanding how to calculate mortgage payment is one of the most practical financial skills you can develop. Whether you're buying your first home or refinancing, knowing the math behind your monthly obligation puts you in control of the negotiation — and your budget.

The standard mortgage payment formula is:

M = P[r(1+r)^n] / [(1+r)^n – 1]

Where:

• M = Monthly payment
• P = Principal loan amount
• r = Monthly interest rate (annual rate ÷ 12)
• n = Total number of payments (loan term in years × 12)

It looks intimidating, but the logic is simple: you're spreading the principal plus all future interest across equal monthly payments so the loan reaches exactly zero on the final payment date.

Use our free Mortgage Calculator to run the numbers instantly without doing any algebra by hand.

Worked Example: $280,000 Loan at 6.5% for 30 Years

Let's make this concrete. Suppose you're buying a $350,000 home, putting 20% down ($70,000), which leaves a $280,000 loan at a 6.5% annual interest rate over 30 years.

Plugging into the formula:

• r = 6.5% ÷ 12 = 0.5417% per month (0.005417 as a decimal)
• n = 30 × 12 = 360 payments

M = 280,000 × [0.005417 × (1.005417)^360] / [(1.005417)^360 – 1]

(1.005417)^360 ≈ 6.848

M = 280,000 × [0.005417 × 6.848] / [6.848 – 1] M = 280,000 × [0.03710] / [5.848] M = 280,000 × 0.006344 M ≈ $1,776/month

Over 30 years you'll pay approximately $359,360 in total — meaning roughly $79,360 goes to interest on top of your $280,000 principal. That's why your interest rate matters enormously.

Monthly Payment Comparison Table

The table below shows estimated monthly payments (principal + interest only, excluding taxes and insurance) at different loan amounts and interest rates:

30-year fixed-rate mortgage. Principal and interest only.

A 1.5 percentage-point difference in rate (5% vs 6.5%) on a $300,000 loan adds $286/month — nearly $103,000 over the life of the loan. Shopping two or three lenders can realistically save you six figures.

Understanding Amortization: Where Your Money Actually Goes

Mortgage amortization means each fixed monthly payment covers both interest and principal, but the ratio shifts dramatically over time.

In the early years of your mortgage, most of each payment is interest. Here's what the split looks like on our $280,000 / 6.5% / 30-year example:

• Month 1: ~$1,517 interest / ~$259 principal
• Year 5 (month 60): ~$1,455 interest / ~$321 principal
• Year 15 (month 180): ~$1,195 interest / ~$581 principal
• Year 25 (month 300): ~$737 interest / ~$1,039 principal
• Month 360 (final): ~$10 interest / ~$1,766 principal

This is why making extra payments in the first 5–10 years is so powerful — every extra dollar goes almost entirely toward principal, which compounds into less future interest.

How Down Payment Size Affects PMI

If you put less than 20% down, most lenders require private mortgage insurance (PMI) — a protection for the lender, paid by you. PMI typically costs 0.5% to 1.5% of the loan balance per year, added to your monthly payment.

On a $300,000 loan at 1% PMI, that's an extra $250/month until you reach 20% equity.

Here's how different down payments affect your picture on a $350,000 home:

• 3.5% down (FHA loan): Loan = $337,750 + mandatory MIP (mortgage insurance premium)
• 10% down: Loan = $315,000 + PMI until 20% equity reached
• 20% down: Loan = $280,000, no PMI
• 25% down: Loan = $262,500, potentially better rate tier at some lenders

The 20% threshold isn't magic — but crossing it eliminates a monthly cost that doesn't build any equity.

The 28% Rule: How Much House Can You Afford?

A widely used affordability benchmark is that total housing costs should be no more than 28% of your gross monthly income. Housing costs include:

• Principal and interest
• Property taxes (typically 1–2% of home value annually, divided by 12)
• Homeowner's insurance (~$150–$200/month for a median-priced home)
• HOA fees (if applicable)
• PMI (if applicable)

If your gross household income is $8,000/month, the 28% rule suggests keeping total housing under $2,240/month. At current rates, that's roughly a $270,000–$290,000 mortgage before adding taxes and insurance.

For a fuller financial picture, also check your debt-to-income ratio (DTI). Most conventional lenders want your total DTI — all debt payments divided by gross income — below 43%, with the best rates reserved for borrowers under 36%.

Factors That Affect Your Mortgage Rate

Your quoted interest rate will differ from published averages based on several personal factors:

• Credit score: Borrowers with 760+ scores routinely get rates 0.5–1.0% lower than those with 680 scores
• Loan-to-value ratio: Bigger down payments typically unlock lower rates
• Loan type: Conventional, FHA, VA, and USDA loans each have different rate structures
• Loan term: 15-year loans typically carry rates 0.5–0.75% lower than 30-year loans
• Points: Paying 1 discount point (1% of loan amount upfront) typically buys the rate down by ~0.25%
• Property type: Primary residences get better rates than investment properties or second homes

Want to model different rate scenarios? Use our free Mortgage Calculator to see how a 0.5% rate difference affects your total cost over time.

Other Calculators You May Need

Before finalizing your home purchase, it's worth understanding the full debt picture. Use our Loan Calculator to model any additional borrowing, or our Savings Calculator to figure out how long it will take to accumulate your down payment at current savings rates.

Conclusion: Key Takeaways

• The mortgage payment formula M = P[r(1+r)^n] / [(1+r)^n–1] produces a fixed monthly payment that pays off principal and interest exactly over the loan term
• On a $280,000 loan at 6.5% for 30 years, expect to pay roughly $1,776/month and approximately $79,000 in total interest
• Rate differences of even 1.5% can add or remove over $100,000 in total interest on a $300,000 loan
• Putting less than 20% down triggers PMI costing $100–$400/month until you reach 20% equity
• Use the 28% rule as a quick affordability check: keep total housing costs below 28% of gross monthly income
• Making extra principal payments early in the loan can dramatically reduce total interest paid

Calculate your exact monthly mortgage payment now →