How to Calculate Mortgage Payments
Your monthly mortgage payment is the single biggest recurring expense for most homeowners. Understanding exactly how it's calculated — and where your money goes each month — puts you in control. In this guide, we break down the formula, walk through a real example, and show you how extra payments can save you thousands.
1. What makes up a mortgage payment
Most people think of their mortgage payment as a single number, but it actually has several components, commonly abbreviated as PITI:
P — Principal
The portion that reduces your loan balance. Early in the loan, this is surprisingly small.
I — Interest
The cost of borrowing money. Early in the loan, this is the majority of your payment.
T — Taxes
Property taxes, often collected monthly by your lender and held in escrow.
I — Insurance
Homeowners insurance (and PMI if your down payment was less than 20%).
Our calculator focuses on the principal and interest portion — the core loan payment. Taxes and insurance vary by location and policy, so you'll want to add those separately for your total monthly cost.
2. The mortgage payment formula
The standard formula for a fixed-rate mortgage monthly payment is:
M = P × [r(1+r)n] / [(1+r)n − 1]
M = monthly payment (principal + interest)
P = loan principal (home price minus down payment)
r = monthly interest rate (annual rate ÷ 12)
n = total number of payments (years × 12)
This formula produces a fixed monthly payment that stays the same for the entire loan term. What changes over time is how much of each payment goes to principal vs. interest.
3. Step-by-step example
Let's calculate the monthly payment for a typical home purchase:
Home price: $350,000
Down payment: $70,000 (20%)
Loan amount (P): $280,000
Interest rate: 6.5% per year
Loan term: 30 years
Step 1: Monthly rate
r = 0.065 / 12 = 0.005417
Step 2: Total payments
n = 30 × 12 = 360
Step 3: Plug into formula
M = 280,000 × [0.005417 × (1.005417)360] / [(1.005417)360 − 1]
M = 280,000 × [0.005417 × 6.9918] / [6.9918 − 1]
M = 280,000 × [0.03788] / [5.9918]
M = 280,000 × 0.006321
M = $1,769.88/month
So the monthly principal and interest payment is $1,769.88. Over 30 years, you'll make 360 payments totaling $637,157 — meaning you'll pay $357,157 in interest on a $280,000 loan. That's more than the original loan amount!
4. How amortization works
Even though your monthly payment stays the same, the split between principal and interest changes dramatically over the life of the loan. This is called amortization.
| Payment | To interest | To principal | Remaining balance |
|---|---|---|---|
| Month 1 | $1,516.67 | $253.21 | $279,746.79 |
| Month 12 | $1,502.21 | $267.67 | $276,797.42 |
| Month 60 | $1,426.06 | $343.82 | $262,860.15 |
| Month 180 | $1,168.94 | $600.94 | $215,000.58 |
| Month 300 | $717.65 | $1,052.23 | $132,138.86 |
| Month 360 | $9.54 | $1,760.34 | $0.00 |
💡 Key insight
In the first payment, 86% goes to interest and only 14% reduces your loan balance. By the last payment, it flips — 99% goes to principal. This front-loaded interest structure is why the early years of a mortgage feel so slow in building equity.
5. The total cost of a mortgage
Understanding the total cost helps put the true expense of homeownership in perspective.
30-year at 6.5%
$357,157
total interest paid
Monthly: $1,770
20-year at 6.5%
$217,272
total interest paid
Monthly: $2,088
15-year at 6.5%
$157,240
total interest paid
Monthly: $2,439
Choosing a 15-year over a 30-year mortgage saves you nearly $200,000 in interest — but the monthly payment is $669 higher. The right choice depends on your cash flow, emergency fund, and other financial goals.
6. How extra payments save you thousands
One of the most powerful mortgage strategies is making extra payments toward your principal. Since extra payments bypass interest and go straight to the balance, even small amounts have an outsized effect.
Example: $200/month extra on a $280,000 loan at 6.5%
Without extra payments
30 years to pay off
Total interest: $357,157
With $200/month extra
~23 years to pay off
Total interest: $264,466
Savings: ~$92,691 in interest and 7 years off the loan! 🎉
Other extra payment strategies:
- Bi-weekly payments: Pay half your monthly payment every two weeks. You end up making 26 half-payments (= 13 full payments) per year instead of 12 — one extra payment annually.
- Annual lump sum: Apply your tax refund, bonus, or other windfall once per year toward the principal.
- Round up: If your payment is $1,770, round up to $2,000. The extra $230/month goes entirely to principal.
7. Factors that affect your payment
Interest rate
high impactEven a 0.5% difference matters enormously over 30 years. On a $280,000 loan, the difference between 6.0% and 6.5% is about $95/month — or $34,200 over the life of the loan.
Loan term
high impactShorter terms mean higher monthly payments but dramatically less total interest. A 15-year loan at the same rate saves nearly 50% in total interest.
Down payment
medium impactA larger down payment reduces the loan principal, which directly reduces both your monthly payment and total interest. Putting 20% down also eliminates PMI (private mortgage insurance).
Credit score
high impactYour credit score is the biggest factor in determining the rate you're offered. An excellent score (750+) can save you 0.5–1.5% compared to a fair score (650–699).
Property taxes
medium impactVary widely by location. Can add $200–$800/month to your actual payment depending on where you buy.
PMI
low impactIf your down payment is less than 20%, expect PMI of 0.5–1% of the loan annually until you reach 20% equity. On a $280,000 loan, that's $117–$233/month.
8. Tips for getting a better mortgage
1Shop around — always
Get quotes from at least 3–5 lenders. Rates can vary significantly, and even a 0.25% difference saves thousands over the life of the loan.
2Improve your credit score first
If your score is below 740, consider spending 3–6 months improving it before applying. Pay down credit cards, fix errors on your credit report, and avoid opening new accounts.
3Consider a 15-year mortgage
If you can afford the higher payment, a 15-year mortgage typically comes with a lower interest rate and saves you hundreds of thousands in interest.
4Make a 20% down payment if possible
Eliminates PMI, reduces your principal, and often qualifies you for better rates. If 20% isn't feasible, aim for the highest down payment you can manage.
5Don't forget closing costs
Budget 2–5% of the home price for closing costs (appraisal, origination fees, title insurance, etc.). These don't reduce your loan but do affect your total out-of-pocket cost.
6Consider refinancing later
If rates drop 0.75–1% below your current rate, refinancing could save you significantly. Run the numbers with our calculator to see if it makes sense.
9. Calculate your own mortgage
Ready to run your own numbers? Our free mortgage calculator shows your monthly payment, full amortization schedule, and interactive charts — so you can see exactly where every dollar goes.