🏡 🏡 How to Calculate Your Monthly Mortgage Payment

The monthly mortgage payment is one of the most important numbers in personal finance. Most people focus on the purchase price of a home, but the monthly payment is what actually shapes your budget for the next 15 to 30 years. Understanding how that number is calculated — and what it includes — helps you make smarter decisions about how much home you can truly afford.

The Mortgage Payment Formula

The base mortgage payment (principal + interest only) is calculated with the standard loan amortization formula:

M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ − 1]

Where:

• M = Monthly payment
• P = Principal (loan amount = home price minus down payment)
• r = Monthly interest rate = Annual rate ÷ 12
• n = Number of monthly payments (loan term × 12)

Worked Example: $350,000 Home, 7% Rate, 30 Years

• Down payment (20%): $70,000 → Loan amount (P): $280,000
• Monthly rate (r): 7% ÷ 12 = 0.5833% = 0.005833
• Payments (n): 30 × 12 = 360
• M = $280,000 × [0.005833 × (1.005833)³⁶⁰] ÷ [(1.005833)³⁶⁰ − 1]
• M = $280,000 × [0.005833 × 8.116] ÷ [8.116 − 1]
• M = $280,000 × 0.04734 ÷ 7.116 = $1,863/month (principal + interest)

Total paid over 30 years: $1,863 × 360 = $670,680 | Total interest: $390,680

PITI: Your Real Monthly Mortgage Payment

The principal + interest calculation above is just the starting point. Your actual monthly payment to the lender typically includes four components, known as PITI:

• P — Principal: The portion that reduces your loan balance
• I — Interest: The cost of borrowing
• T — Property Taxes: Typically collected monthly by your lender and paid to the local government annually. Average US rate: 1.1% of home value per year. On a $350,000 home: $350,000 × 1.1% ÷ 12 = $321/month
• I — Insurance: Homeowners insurance, required by all lenders. Average US cost: about $200/month, but varies widely by location and home value.

Total PITI payment for our example: $1,863 + $321 + $200 = ~$2,384/month

Private Mortgage Insurance (PMI)

If your down payment is less than 20% of the purchase price, lenders typically require PMI — insurance that protects the lender (not you) if you default. PMI typically costs 0.46%–1.5% of the loan amount annually.

On a $280,000 loan at 1% PMI: $280,000 × 1% ÷ 12 = $233/month extra.

PMI can be cancelled once your equity reaches 20% of the original purchase price — typically after several years of payments and/or home price appreciation. Request cancellation in writing when you reach 20% equity; lenders must remove it automatically at 22% equity.

The 28/36 Affordability Rule

Financial experts and most lenders use the 28/36 rule to determine how much mortgage is affordable:

• 28% rule: Your monthly housing costs (PITI) should not exceed 28% of your gross monthly income.
• 36% rule: Your total monthly debt payments (housing + all other debts) should not exceed 36% of gross monthly income.

Example: Gross monthly income = $7,000

• Maximum housing payment (28%): $7,000 × 0.28 = $1,960/month
• Maximum total debt (36%): $7,000 × 0.36 = $2,520/month
• If you have $400/month in car loan and student loan payments, your maximum mortgage is $2,520 − $400 = $2,120/month

Note: FHA loans allow a 31/43 ratio. Some conventional lenders approve up to 43% back-end DTI for strong borrowers. The 28/36 rule is a guideline — your comfort level matters too.

Fixed-Rate vs. Adjustable-Rate Mortgages (ARM)

Fixed-Rate Mortgage

The interest rate — and therefore the principal + interest payment — stays the same for the entire loan term. Predictable, safe, ideal for long-term homeowners. Currently the most popular choice in the US.

Adjustable-Rate Mortgage (ARM)

The interest rate is fixed for an initial period (typically 3, 5, or 7 years), then adjusts annually based on a market index. ARMs typically start with lower rates than 30-year fixed mortgages. A 5/1 ARM means the rate is fixed for 5 years, then adjusts every 1 year. Risk: if rates rise significantly, your payment could increase substantially after the fixed period ends.

15-Year vs. 30-Year Mortgage: The Real Trade-off

On the same $280,000 loan:

How Your Credit Score Affects Your Rate

Mortgage rates vary significantly by credit score. According to CFPB data, on a $300,000 30-year mortgage:

• 760+ credit score: ~7.0% rate → $1,996/month
• 700–759 score: ~7.2% rate → $2,037/month
• 650–699 score: ~7.7% rate → $2,131/month
• 620–649 score: ~8.4% rate → $2,284/month

A 100-point credit score improvement can save $100–$300/month in mortgage payments — that's $36,000–$108,000 over 30 years. Improving your score before applying is one of the highest-return financial moves available to homebuyers.

Closing Costs: The Upfront Payment Often Forgotten

Beyond the down payment, buying a home involves closing costs typically ranging from 2%–6% of the loan amount, including:

• Origination fees and points
• Appraisal fee ($300–$700)
• Title insurance ($1,000–$2,500)
• Attorney/escrow fees
• Prepaid property taxes and insurance

On a $280,000 loan, closing costs of 3% add $8,400 to your upfront costs. Budget for this separately from your down payment.