PITI, Explained: The Four Parts of Your Mortgage Payment and the 28/36 Rule That Decides How Much House You Can Afford

The mortgage calculator said $1,850 a month, so you offered with confidence — and then the Loan Estimate arrived showing $2,640 coming out of your checking account every month. Nothing was misquoted. The calculator showed principal and interest only, while your lender underwrote something bigger: principal, interest, taxes, and insurance together, plus every other monthly debt you carry, measured against your gross income with two ratios that quietly decide your maximum purchase price. If you shop for a house using the principal-and-interest number alone, you will fall in love about 30 percent above what a lender will actually approve.

PITI is the acronym lenders, servicers, and closing documents use for those four components of a monthly mortgage payment. Understanding each one — and the 28/36 debt-to-income rule built on top of them — tells you what your real monthly cost will be, how much house your income supports, and which levers actually move your approval number. This guide breaks down all four parts, explains how escrow handles the tax and insurance slices, walks through the front-end and back-end ratios with real numbers, and shows how to track the whole payment cleanly in your books.

The Four Letters: What PITI Actually Stands For​

PITI stands for Principal, Interest, Taxes, and Insurance. The first two repay your loan; the last two are collected alongside them so the bills that protect the lender's collateral never go unpaid.

P: Principal​

Principal is the portion of each payment that pays down the loan balance itself. On a standard fixed-rate amortizing mortgage, the principal slice starts small and grows over time: early payments are mostly interest, while later payments are mostly principal. Every dollar of principal you pay is a dollar of equity you gain and a dollar that stops accruing interest in every future month.

This is also the only one of the four components you directly control after closing. Extra principal payments — a little more each month, one extra payment a year — shorten the loan and cut total interest, because interest is always computed on the remaining balance.

I: Interest​

Interest is the lender's charge for the use of its money, expressed as an annual rate but computed monthly on your outstanding balance. It is the largest slice of PITI in the early years of most 30-year loans: at a 7 percent rate on a $400,000 loan, your first monthly payment of about $2,661 contains roughly $2,328 of interest and only $333 of principal.

Your interest cost depends on the rate you lock, the loan term, and how fast you pay principal down. Refinancing changes this slice; nothing else in PITI responds to rate moves.

T: Taxes (Property Taxes)​

Property taxes are levied by your county or municipality, usually once or twice a year, based on your home's assessed value and the local tax rate. A 1.1 percent effective rate on a $500,000 home means $5,500 a year, or about $458 a month folded into your payment.

Two things surprise first-time buyers here. First, property taxes are reassessed: buy a home long held by one owner and the assessed value can jump to your purchase price, repricing the tax bill well above what the seller paid. Second, taxes rise over time while principal and interest stay fixed, so the T slice is the main reason a "fixed" mortgage payment still creeps upward year after year.

I: Insurance (Homeowners Insurance)​

Homeowners insurance protects the house — the lender's collateral — against fire, wind, liability claims, and the other perils in the policy. Lenders require it from day one, and if your coverage lapses the servicer will buy force-placed insurance for you at a far worse price.

Like taxes, premiums are billed annually but collected monthly through your payment, and like taxes they have been climbing fast: replacement-cost inflation and regional catastrophe risk have pushed many homeowners' premiums up by double digits in a single renewal. If your monthly payment jumps at the annual escrow review, the insurance renewal is the first place to look.

PITI vs. Your Full Housing Payment: What Else Gets Added​

PITI is the core, but it is rarely the whole check you write. Depending on your loan and property, several more items stack on top — and lenders count all of them when they measure your housing ratio:

• Private mortgage insurance (PMI) or FHA mortgage insurance premium (MIP). With less than 20 percent down on a conventional loan, you pay PMI until you reach 20 percent equity (you can request cancellation there; it drops automatically at 78 percent of the original value). FHA loans charge MIP differently: with less than 10 percent down it lasts the life of the loan, and escaping it means refinancing into a conventional loan.
• HOA dues. Condo and planned-community assessments count dollar for dollar in your housing ratio, and special assessments can land without warning. A $350 monthly HOA payment reduces your approved purchase price by roughly $50,000 at typical rates — lenders treat it as committed housing cost.
• Flood insurance. Required if the home sits in a high-risk flood zone, and priced separately from homeowners insurance. In coastal and riverine markets this can rival the tax slice.
• Supplemental property taxes. Many buyers in states like California get a separate supplemental tax bill after purchase covering the reassessment gap. It is not in your escrow calculation at closing, so budget for it out of pocket in year one.

When a lender says "housing expense," it means PITI plus every applicable item above. The rich detail matters because each one is a lever: a house with low taxes and no HOA can cost you less per month than a cheaper house with high taxes and a $400 assessment.

The Escrow Account: Where the T and the I Go​

Unless you waive escrow — typically allowed only with at least 20 percent equity — your servicer collects one-twelfth of the coming year's property taxes and insurance premiums with each monthly payment and holds the money in an escrow account (sometimes called an impound account). When the county tax bill or the insurance renewal comes due, the servicer pays it from that account on your behalf.

Once a year the servicer runs an escrow analysis: it compares what it collected against what it actually paid out, then resets your monthly payment for the next twelve months. Three outcomes are possible:

• No change, when last year's estimates matched reality.
• A shortage, when taxes or premiums rose. The servicer spreads the shortfall over the next year — and this is the mechanism behind the dreaded "my fixed mortgage payment went up $180." The loan didn't change; the escrow slice did.
• A surplus, when estimates overshot. Small overages are applied to future payments; larger ones come back as a refund check.

Federal law caps how much cushion a servicer may hold: under RESPA, the escrow balance may not exceed one-sixth of the year's total disbursements — about two months of escrow payments — above what is needed to pay bills on time. If your analysis shows the servicer sitting on far more than that, the math deserves a phone call.

The 28/36 Rule: Front-End vs. Back-End Ratios​

With PITI defined, the 28/36 rule is simple arithmetic. Lenders measure two debt-to-income (DTI) ratios, both using gross (pre-tax) monthly income:

• Front-end ratio (housing ratio): total monthly housing expense divided by gross monthly income. The classic guideline caps it at 28 percent.
• Back-end ratio (total DTI): housing expense plus all recurring monthly debts — car loans, student loans, credit-card minimums, child support, personal loans — divided by gross monthly income. The classic guideline caps it at 36 percent.

Take a household earning $120,000 a year, or $10,000 a month before tax. The 28/36 rule says housing expense should stay at or under $2,800 a month, and housing plus all other minimum debt payments should stay at or under $3,600 a month. If that household carries $700 a month in car and student-loan payments, the back-end cap leaves $2,900 for housing — so the front-end cap of $2,800 still binds, but only barely. Add a $400 car lease and the back-end math, not the front-end math, becomes the ceiling that shrinks the approved loan.

Note what the ratios ignore: income tax, groceries, utilities, childcare, retirement savings, and everything else you actually spend. The guidelines measure default risk for the lender, not comfort for you. Many buyers find that a payment at the full 28 percent leaves less breathing room than expected once real life is accounted for — which is why running your own budget alongside the lender's ratios is the move, not a substitute for it.

What the Limits Really Are by Loan Type​

The 28/36 figures are the textbook benchmark, but actual caps vary by loan program — and every program stretches higher for strong files with compensating factors like high credit scores, cash reserves, or a conservative loan-to-value ratio:

Two practical takeaways hide in this table. First, FHA's higher ratios are a genuine affordability tool for buyers with moderate incomes and smaller down payments — the program is designed to approve files conventional underwriting would decline. Second, "up to 50 percent" is not a target: a back-end ratio near half your gross income means half of every pre-tax dollar is already spoken for before food, taxes, or savings. Approval and affordability are different questions, and only you answer the second one.

How to Run Your Own Numbers Before a Lender Does​

Do this before you tour a single house, because it takes ten minutes and prevents the most expensive emotion in real estate: attachment to a price you cannot finance.

1. Start with gross monthly income. Salary divided by 12, plus documented bonus, commission, rental, or self-employment income averaged the way your lender will average it (usually two years of history). A $120,000 salary is $10,000 a month.
2. Multiply by 0.28 for your housing ceiling. That $10,000 income supports about $2,800 a month in total housing expense — PITI plus PMI, HOA, and flood insurance if they apply.
3. Add up minimum payments on every debt on your credit report, plus child support and any required payments that don't appear there. Suppose they total $650 a month.
4. Multiply income by 0.36 and subtract the debts. $3,600 minus $650 leaves $2,950 for housing. Your ceiling is the lower of the two numbers: $2,800 from the front-end ratio.
5. Work backward to a purchase price. Subtract your best estimates of monthly taxes, insurance, PMI, and HOA for your target area from the ceiling — say $2,800 minus $460 taxes, $180 insurance, $150 PMI, and $0 HOA leaves $2,010 for principal and interest. At 7 percent on a 30-year loan, $2,010 a month in principal and interest supports roughly a $302,000 loan; add your down payment to get your price ceiling.

The step most buyers skip is step 5's subtraction. Every dollar of taxes, insurance, or HOA comes straight out of the principal-and-interest budget, which is why two identical paychecks buy very different houses in New Jersey and Tennessee.

Common Mistakes That Blow Up the Math​

• Shopping on principal and interest alone. Online calculators default to P&I; always add local taxes and insurance before comparing the result to your budget.
• Taking on new debt before closing. Lenders re-pull credit before funding. A new car loan or furniture-store account between approval and closing can push your back-end ratio over the cap and kill the loan days before move-in.
• Forgetting the reassessment jump. The seller's tax bill reflects the seller's assessed value. Ask the county assessor what the home will be assessed at after your purchase, and underwrite that number.
• Ignoring HOA trajectory. A $250 HOA with a history of special assessments is riskier than a $350 HOA with healthy reserves. Read two years of meeting minutes before you count the dues as stable.
• Assuming the payment is fixed forever. Principal and interest are fixed on a fixed-rate loan; taxes and insurance are not. Budget a few percent of annual growth into the escrow slice so the yearly analysis never ambushes you.
• Waiving escrow without a plan. Paying taxes and insurance yourself in two lump sums a year demands discipline and a funded sinking account. Miss the county deadline and penalties accrue fast.

Tracking PITI in Your Books​

One mortgage payment is really four economic events wearing a trench coat: debt reduction, interest expense, a tax prepayment, and an insurance prepayment. Booking the whole payment as a single "mortgage expense" overstates your costs and hides your growing escrow balance — and it makes the annual escrow analysis impossible to reconcile. Split it instead:

2026-11-01 * "Monthly mortgage payment"
  Assets:Checking                   -2,650.00 USD
  Liabilities:Mortgage:Home-Loan       1,200.00 USD
  Expenses:Interest:Mortgage             800.00 USD
  Assets:Escrow:Mortgage                 650.00 USD
 
2026-12-10 * "County property tax paid from escrow"
  Expenses:Taxes:Property               5,400.00 USD
  Assets:Escrow:Mortgage               -5,400.00 USD

The payment posting reduces the loan, records the interest, and parks the tax-and-insurance slice in an escrow asset account. When the servicer actually pays the county or the insurer, a second entry moves the money from escrow to the real expense. Your escrow account balance should then track the servicer's reported balance within a payment or two — and any shortage notice becomes a reconciling item you can verify rather than a number you take on faith. The Beancount documentation covers account structure and balance assertions in more depth if you want to automate that check.

At tax time this split pays off again: mortgage interest and property taxes are itemized-deduction candidates, while principal repayment is not deductible at all. With the components separated all year, your Schedule A practically writes itself.

Your next useful step is the ten-minute exercise from the section above: take your gross monthly income, multiply by 0.28, subtract realistic taxes, insurance, and HOA for the neighborhoods you are actually considering, and convert what remains into a loan amount. That number — not the preapproval letter's maximum, and not the calculator's principal-and-interest figure — is your real budget. Shop under it and every part of the process, from the offer to the annual escrow analysis, gets calmer.