Most homebuyers know their monthly payment number long before they understand where it came from. Lenders hand you a figure, you squint at it, decide it sounds roughly affordable, and sign 360 pieces of paper. But that single number is built from several distinct components — and knowing what each one is (and how to change it) can save you tens of thousands of dollars over the life of your loan.
This guide walks through the exact formula, breaks down every component, and shows you real numbers at multiple price points so nothing comes as a surprise at closing.
The Two Types of Mortgage Payments
When people say "monthly mortgage payment," they're usually talking about one of two things:
- P&I only — Principal and interest. Just the loan repayment cost. This is what amortization tables show.
- PITI — Principal, Interest, Taxes, and Insurance. The real all-in monthly cost, and what lenders use to evaluate whether you can actually afford the home.
On top of PITI, some owners also pay PMI (Private Mortgage Insurance, if you put down less than 20%) and HOA fees. We'll cover all of it.
Step 1: Calculate Principal and Interest (P&I)
The P&I payment uses the standard loan amortization formula. It looks scarier than it is:
Worked Example: $400,000 Home, 2026 Rates
- Home price: $400,000 | Down payment: 20% = $80,000
- Loan amount (P): $320,000
- Rate: 6.75% annual → monthly r = 0.005625
- Term: 30 years → n = 360 payments
In your very first payment of $2,076, only about $271 goes toward paying down the actual loan — the remaining $1,800 is pure interest. By year 20, that flips: over $1,000 per payment reduces principal. Early payments are mostly renting money from the bank. This is why extra early payments have an outsized effect on total interest paid.
Step 2: Add Property Tax
Property tax is billed annually but collected monthly into an escrow account by your lender. Rates vary enormously — under 0.3% in Hawaii, over 2.2% in New Jersey — so always look up your specific county's rate.
Formula: (Home value × tax rate) ÷ 12 = monthly escrow
Example: $400,000 home × 1.2% tax rate = $4,800/year → $400/month
Step 3: Add Homeowner's Insurance
Lenders require hazard insurance to protect their collateral. The national average in 2026 runs about $1,400–$1,800/year for a $400,000 home — roughly $117–$150/month. Like taxes, it's typically escrowed.
Step 4: Add PMI (If Your Down Payment Is Under 20%)
Private Mortgage Insurance protects the lender — not you — if you default. It's required by most conventional lenders when your down payment is less than 20%.
- Typical cost: 0.5%–1.5% of the loan amount per year
- On a $320,000 loan at 1%: $3,200/year → $267/month
- Cancels automatically at 22% equity; you can request removal at 20%
PMI is a meaningful cost — $267/month is $3,200/year you're paying for nothing. Putting 20% down is the cleanest way to avoid it, but if you can't, get it removed the moment you hit 20% equity (request a new appraisal if your home has appreciated).
Step 5: Add HOA Fees (If Applicable)
Condos, townhomes, and many planned communities come with monthly HOA fees ranging from $100 in modest subdivisions to $1,000+ in luxury developments. HOA fees aren't part of your mortgage payment, but lenders do include them in your debt-to-income ratio calculation — meaning they reduce how much house you can qualify for.
The Full Monthly Payment Breakdown
Here's what the total PITI looks like at common price points at 6.75% with 20% down and a 1.2% tax rate:
| Component | $300K Home | $400K Home | $600K Home |
|---|---|---|---|
| Principal & Interest (6.75%, 30yr) | $1,557 | $2,076 | $3,114 |
| Property Tax (1.2% rate) | $300 | $400 | $600 |
| Homeowner's Insurance | $100 | $130 | $175 |
| PMI (if <20% down, ~1%/yr) | $250 | $267 | $400 |
| Total PITI (no PMI) | $1,957 | $2,606 | $3,889 |
| Total with PMI | $2,207 | $2,873 | $4,289 |
How Interest Rate Affects Your Payment
This is the table worth printing out before you go rate shopping. On a $320,000 loan over 30 years:
| Rate | Monthly P&I | Total Interest Paid |
|---|---|---|
| 5.5% | $1,817 | $333,951 |
| 6.0% | $1,919 | $370,840 |
| 6.75% | $2,076 | $427,360 |
| 7.5% | $2,238 | $485,708 |
| Gap: 5.5% vs 7.5% | $421/mo more | $151,757 more |
A 2% rate difference costs over $150,000 over the life of the loan. Spending a few hours shopping multiple lenders — or paying a mortgage broker — is almost always worth it. Each 0.5% rate reduction saves roughly $38,000 over 30 years on a $320K loan.
Mortgage Points: Paying to Lower Your Rate
One option many buyers overlook: you can pay "discount points" upfront to permanently reduce your interest rate. One point = 1% of the loan amount = roughly 0.25% rate reduction.
On a $320,000 loan: 1 point costs $3,200 and reduces your rate by ~0.25%, saving about $54/month. Break-even: $3,200 ÷ $54 = 59 months (~5 years). If you plan to keep the home longer than that, buying points pays off. If you might refinance or move within 5 years, skip them.
15-Year vs. 30-Year Mortgage
The most impactful choice after your rate. On a $320,000 loan:
- 30-year at 6.75%: $2,076/month → $427,360 total interest
- 15-year at 6.0% (15-yr rates are typically lower): $2,703/month → $166,504 total interest
The 15-year costs $627 more per month but saves $260,856 in total interest. If your budget can handle the higher payment, it's one of the best wealth-building moves available — you own the home free and clear in half the time and pay roughly 60% less interest.
Adjustable-rate mortgages (ARMs) start with a lower fixed rate for 5, 7, or 10 years, then adjust annually based on market rates. They can be smart if you're certain you'll sell or refinance before the adjustment period. But always model the worst-case rate scenario before signing — "it'll be fine" is how people get into payment shock.
What Lenders Look At: Debt-to-Income Ratio
Most conventional lenders want your total housing payment (PITI + HOA) at no more than 28% of gross monthly income, and total debt (housing + car + student loans + credit cards) at no more than 43%.
| Annual Income | Max Housing Payment (28%) | Approximate Home Price |
|---|---|---|
| $60,000 | $1,400/mo | ~$175,000–$210,000 |
| $80,000 | $1,867/mo | ~$230,000–$280,000 |
| $100,000 | $2,333/mo | ~$290,000–$350,000 |
| $150,000 | $3,500/mo | ~$440,000–$530,000 |
These ranges assume 20% down, 6.75% rate, and 1.2% property tax. Your actual numbers will vary — use our mortgage calculator to plug in your specific situation.