How to Calculate Your Monthly Mortgage Payment (Step-by-Step)

The Mortgage Payment Formula Explained

Your monthly principal-and-interest payment is calculated with the standard amortization formula:

This formula calculates only principal and interest. Your actual payment generally includes taxes and insurance too. For complete budgeting, use the full PITI view in the NerdCalc Mortgage Calculator.

A Real-World Example

Assume a $350,000 home, 20% down payment, 6.5% rate, and a 30-year fixed term.

Step 1: Principal

$350,000 * 0.80 = $280,000

Step 2: Monthly Interest Rate

6.5% / 12 = 0.5417% = 0.005417

Step 3: Number of Payments

30 * 12 = 360

Step 4: Solve Formula

M ~= $1,770 per month (principal and interest only)

If property taxes are $350/month and insurance is $125/month, total monthly housing cost is roughly $2,245/month.

What Is Included in Monthly Payment (PITI)

Principal

The portion that reduces loan balance. Early payments apply less to principal than most buyers expect.

Interest

The lender's borrowing charge. On larger balances and higher rates, this is usually the biggest early-year component.

Taxes

Local property taxes vary by location and are often escrowed monthly by the lender. For broader debt planning, compare with the General Loan Calculator.

Insurance

Homeowners insurance and sometimes flood or hazard coverage depending on property location.

How Rate, Term, and Down Payment Change the Payment

Interest Rate Impact (on $280,000, 30-year)

• 5.5%: about $1,589/month
• 6.5%: about $1,770/month
• 7.5%: about $1,958/month

A 1-point rate shift can move payment by roughly $180/month and change lifetime interest dramatically.

Loan Term Impact (on $280,000 at 6.5%)

• 30-year: about $1,770/month, about $357,200 total interest
• 15-year: about $2,441/month, about $159,380 total interest

Shorter terms raise monthly cash flow pressure but can save six figures in long-term interest.

Down Payment Impact (on $350,000 at 6.5%, 30-year)

• 5% down: about $2,102/month plus PMI
• 10% down: about $1,991/month plus PMI
• 20% down: about $1,770/month, typically no PMI

When down payment is below 20%, private mortgage insurance usually increases effective monthly cost.

How Amortization Changes Where Your Money Goes

Fixed-rate mortgage payments stay constant, but the principal-interest mix shifts over time. Early payments are interest-heavy. Later payments are principal-heavy.

That is why extra principal paid early often has outsized impact. Even $100/month extra can shorten payoff and reduce total interest significantly.

For a full amortization walkthrough, see our Mortgage Calculator Guide.

Tips to Lower Your Monthly Payment

1. Improve credit score to qualify for better rates.
2. Increase down payment to shrink loan size and avoid PMI.
3. Compare lender quotes on the same day.
4. Evaluate term trade-offs between monthly payment and lifetime cost.
5. Review points and fees before choosing a lower note rate.