How to Calculate Your Mortgage Payment (Step-by-Step)
When you look at a monthly mortgage payment, you're really looking at four separate pieces stacked together: principal, interest, property taxes, and insurance (often called PITI). Understanding each one is the difference between being surprised by a bill and knowing exactly what you're paying for.
Here's how the math actually works — and how to run the numbers for your own loan.
The Four Parts of a Mortgage Payment (PITI)
- Principal — The amount you borrowed. This is the "loan amount" itself, before any interest is added.
- Interest — The cost of borrowing, charged as a percentage of your remaining balance.
- Property taxes — Collected by your local government and often rolled into your monthly payment.
- Insurance — Homeowners insurance, plus PMI (private mortgage insurance) if your down payment is under 20%, and possibly HOA fees.
Lenders call this bundle "PITI" because it's the full amount you pay each month — not just the loan itself.
The Mortgage Payment Formula
The core formula for principal and interest is:
M = P × [ r(1 + r)ⁿ ] ÷ [ (1 + r)ⁿ − 1 ]
Where:
- M = your monthly payment
- P = the loan principal (amount borrowed)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of payments (years × 12)
Don't worry about doing this by hand — the formula is here so you can see why the numbers come out the way they do. The important part is understanding what it means: most of your early payments go toward interest, not principal.
A Real Example: $300,000 Home, 6.5% Interest, 30 Years
Let's run a realistic scenario:
| Item | Value |
|---|---|
| Home price | $300,000 |
| Down payment (20%) | $60,000 |
| Loan amount | $240,000 |
| Interest rate | 6.5% |
| Term | 30 years |
Monthly principal & interest = $1,517
But that's not the whole picture. Add:
- Property tax (~$250/month)
- Homeowners insurance (~$100/month)
Total monthly payment ≈ $1,867
Over 30 years, you'll pay about $546,000 total — meaning roughly $306,000 in interest alone. That's the number most people never see. The interest can cost more than the house.
💡 Try it yourself: Use our free mortgage calculator to enter your own numbers and see the full breakdown instantly — including the total interest you'll pay.
Why Early Payments Are Mostly Interest
This is the part that surprises most first-time buyers. In month one of the example above, roughly $1,300 of your $1,517 payment goes to interest, and only about $217 reduces the loan.
By year 15, that ratio has flipped. This is called amortization — the gradual shift from interest-heavy to principal-heavy payments over the life of the loan.
3 Ways to Lower Your Mortgage Payment
- Make a bigger down payment — Every dollar down is a dollar you don't pay interest on for 30 years.
- Buy down your interest rate — Even 0.5% less can save tens of thousands over the loan.
- Choose a shorter term — A 15-year loan has a higher monthly payment but dramatically less total interest.
Frequently Asked Questions
How is my mortgage payment calculated? It's the sum of principal, interest, taxes, and insurance (PITI). The principal and interest portion uses the amortization formula above; taxes and insurance depend on your property and lender.
Why does my payment include taxes and insurance? Most lenders collect these monthly and hold them in an escrow account, then pay the bills for you when they come due. It protects the lender and spreads your costs evenly across the year.
What is PMI and when do I pay it? Private mortgage insurance is required on most loans when your down payment is under 20%. It typically costs 0.5%–1% of the loan amount per year, added to your monthly payment.
Does a lower interest rate always mean a lower payment? Usually, yes — but the loan term matters more than people think. A 15-year loan at a slightly higher rate can still cost you far less in total interest than a 30-year loan at a lower rate.
Ready to see your own numbers? Open the RateLedger mortgage calculator and get a full payment breakdown in seconds.