How to Calculate Mortgage Payment: Formula & Examples

The Mortgage Payment Formula

Your monthly mortgage payment (principal and interest only) is calculated using this formula:

M = P × [r(1+r)^n] / [(1+r)^n - 1]

Where:

• M = monthly payment
• P = principal (loan amount after down payment)
• r = monthly interest rate (annual rate / 12)
• n = total number of payments (years × 12)

Step-by-Step Example

Suppose you are buying a $350,000 home with a 20% down payment, a 30-year term, and a 6.5% annual interest rate.

1. Calculate the principal: $350,000 − 20% = $350,000 − $70,000 = $280,000
2. Monthly interest rate: 6.5% / 12 = 0.065 / 12 = 0.005417
3. Number of payments: 30 × 12 = 360
4. Apply the formula:

   M = 280,000 × [0.005417(1.005417)^360] / [(1.005417)^360 - 1]
   M = 280,000 × [0.005417 × 6.9913] / [6.9913 - 1]
   M = 280,000 × 0.03787 / 5.9913
   M = 280,000 × 0.006321
   M ≈ $1,770

Your monthly principal and interest payment would be approximately $1,770. Note that your actual housing payment will also include property taxes, homeowners insurance, and possibly PMI (private mortgage insurance) if your down payment is less than 20%.

Factors That Affect Your Payment

Interest Rate

Even a small change in interest rate has a big impact. On a $280,000 loan over 30 years, the difference between 6% and 7% is roughly $186 per month — over $67,000 over the life of the loan.

Loan Term

A 15-year mortgage has higher monthly payments but dramatically lower total interest. On the same $280,000 loan at 6.5%, a 15-year term costs about $2,440/month but saves over $170,000 in interest compared to a 30-year term.

Down Payment

A larger down payment reduces the principal, lowers monthly payments, may qualify you for a better interest rate, and eliminates PMI if you put down 20% or more.

Property Taxes and Insurance

These are often bundled into your monthly payment through an escrow account. They can add $200 to $800+ per month depending on your location and coverage.

Tips for Getting a Better Mortgage

1. Improve your credit score before applying — even 20 points can unlock a lower rate.
2. Shop multiple lenders and compare APR (not just the rate).
3. Consider points — paying upfront "discount points" to lower your rate makes sense if you plan to stay long-term.
4. Save for a larger down payment to reduce both your payment and total interest.
5. Get pre-approved to know your budget and strengthen your offer.

Conclusion

Understanding the mortgage payment formula empowers you to compare loan options, negotiate with lenders, and plan your budget with confidence. Crunch the numbers yourself with our Mortgage Calculator and see how different scenarios affect your monthly payment.