How to Calculate Your Monthly Mortgage Payment: A Complete Guide

Buying a home is one of the biggest financial decisions you'll ever make — and your monthly mortgage payment will be one of your largest monthly expenses for decades. Understanding exactly how it's calculated helps you plan, negotiate, and choose the right loan.

What Makes Up a Monthly Mortgage Payment?

Most people think of a mortgage payment as simply principal plus interest. In reality, it typically has four components — abbreviated as PITI:

• Principal — The portion that reduces your loan balance
• Interest — The lender's cost for lending you money
• Taxes — Property taxes (usually 1/12 of annual amount)
• Insurance — Homeowners insurance and, if required, PMI

The Mortgage Payment Formula

The core formula for principal and interest 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)

Example Calculation

Let's say you borrow $350,000 at 6.5% annual interest for 30 years:

• P = $350,000
• r = 6.5% ÷ 12 = 0.5417% = 0.005417
• n = 30 × 12 = 360 payments

Plugging into the formula: M = $2,212.24/month (principal + interest only).

How to Lower Your Monthly Payment

Several strategies can meaningfully reduce what you pay each month:

1. Make a larger down payment — Reduces the principal and may eliminate PMI
2. Choose a longer loan term — 30 years vs 15 years lowers monthly payments (but increases total interest)
3. Improve your credit score — Even 0.5% less interest on a $300,000 loan saves $100+/month
4. Shop multiple lenders — Rates vary significantly between institutions
5. Buy discount points — Pay upfront to permanently reduce your interest rate

Understanding Amortization

In the early years of your mortgage, the majority of each payment goes toward interest — not principal. This is called amortization. Over time, this ratio shifts: by year 20 of a 30-year mortgage, more than half your payment reduces the principal.

Use our Mortgage Calculator to see the full amortization schedule for your specific loan.

Private Mortgage Insurance (PMI)

If your down payment is less than 20%, most conventional loans require PMI. This typically adds 0.5%–1.5% of the loan amount per year to your monthly payment. On a $350,000 loan, that's $145–$438/month extra.

PMI is automatically cancelled once you reach 20% equity (22% by law under the Homeowners Protection Act).