Before you sign anything, you need to know exactly what your monthly mortgage payment will be — and how much of it goes to interest vs. principal. This guide walks you through the formula, gives you clear examples, and shows you how to run the numbers yourself in under a minute.
What Makes Up a Mortgage Payment?
Your monthly mortgage payment typically consists of four parts, often called PITI:
- Principal — the portion that reduces your loan balance
- Interest — the lender’s fee for borrowing money
- Taxes — property taxes, usually held in escrow
- Insurance — homeowner’s insurance and possibly PMI
Most calculators (including ours) calculate P+I. Taxes and insurance vary by location.
The Mortgage Payment Formula
The standard fixed-rate mortgage formula is:
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
- M = monthly payment
- P = loan principal (amount borrowed)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of payments (years × 12)
Step-by-Step Example
Let’s say you borrow $300,000 at 7% annual interest for 30 years:
- P = $300,000
- r = 7% ÷ 12 = 0.5833% = 0.005833
- n = 30 × 12 = 360 payments
- M = 300,000 × [0.005833 × (1.005833)³⁶⁰] / [(1.005833)³⁶⁰ − 1]
- Monthly Payment ≈ $1,996
Over 30 years, you’ll pay $718,560 total — meaning $418,560 in interest alone on a $300,000 loan.
How Interest Rate Affects Your Payment
| Loan Amount | Rate | Term | Monthly Payment |
|---|---|---|---|
| $200,000 | 6% | 30 yr | $1,199 |
| $200,000 | 7% | 30 yr | $1,331 |
| $300,000 | 6% | 30 yr | $1,799 |
| $300,000 | 7% | 30 yr | $1,996 |
| $400,000 | 7% | 30 yr | $2,661 |
15-Year vs 30-Year Mortgage
A 15-year mortgage has a higher monthly payment but saves a massive amount in total interest. On a $300,000 loan at 7%: the 30-year costs $418,560 in interest; the 15-year costs about $185,000 — saving you over $230,000.
Tips to Lower Your Mortgage Payment
- Make a larger down payment to reduce the principal
- Shop for the lowest interest rate (even 0.5% matters enormously)
- Choose a longer term (but remember you pay more interest overall)
- Improve your credit score before applying
- Consider buying points to lower your rate
Calculate Your Mortgage Payment Now
Don’t do the math manually — our free calculator gives you an instant breakdown of monthly payment, total interest, and amortization schedule.
What is the formula for a monthly mortgage payment?
The formula is M = P[r(1+r)^n] / [(1+r)^n – 1], where P is the loan principal, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments.
How does a larger down payment affect my mortgage?
A larger down payment reduces your loan principal, which lowers both your monthly payment and total interest paid over the life of the loan. It may also help you avoid paying private mortgage insurance (PMI).
Can I pay off my mortgage early?
Yes. Making extra payments toward the principal reduces your balance faster and saves significant interest over the life of the loan. Check with your lender first to confirm there are no prepayment penalties.
How to calculate a monthly mortgage payment manually using the standard formula.
Determine the loan principal
Subtract your down payment from the home purchase price. This is the amount you are borrowing (P).
Convert the annual rate to a monthly rate
Divide the annual interest rate by 100 to get a decimal, then divide by 12 to get the monthly rate (r). For example, 6.5% becomes 0.065 / 12 = 0.005417.
Calculate the number of payments
Multiply the loan term in years by 12 to get the total number of monthly payments (n). For a 30-year loan: 30 × 12 = 360.
Apply the mortgage formula
Use M = P[r(1+r)^n] / [(1+r)^n – 1] to calculate your monthly payment.
Use the calculator to verify
Enter your values into the Mortgage Calculator on this site to instantly verify your result and see a full amortization breakdown.
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