The four components
PITI is the number a lender underwrites and the number that leaves your account: principal, interest, taxes and insurance. Add association dues and it becomes PITIA. Quotes that advertise only principal and interest are describing perhaps seventy percent of what you will actually pay.
The split matters because the components behave differently. Principal and interest are fixed for the life of a fixed-rate loan. Taxes and insurance are not fixed at all — they follow assessed value and the insurance market, and they are the reason a payment quoted at closing is not the payment three years later.
The amortization formula
Principal and interest use the standard annuity formula: M = P × [ r(1+r)ⁿ ] / [ (1+r)ⁿ − 1 ], where P is the loan amount, r is the annual rate divided by twelve, and n is the number of monthly payments.
Worked: a $240,000 loan at 7.5 percent over thirty years gives r = 0.00625 and n = 360. (1.00625)³⁶⁰ is about 9.4204, so M = 240,000 × (0.00625 × 9.4204) ÷ (9.4204 − 1) = $1,678 per month. Add $550 of monthly tax and $150 of insurance and the PITI is $2,378.
The formula is exact. Every dollar of imprecision in your payment estimate comes from the inputs — particularly the tax rate, which people routinely guess at.
Property tax varies more than anything else
Effective property tax rates range from well under one percent to well over two and a half percent depending on state, county and municipality. On a $250,000 property that is a spread of more than $300 a month — larger than most of the rate shopping people agonise over.
Texas is the instructive case: no state income tax, and effective rates commonly in the 1.8 to 2.5 percent range once school, county, city and special districts stack. A San Antonio property at 2.2 percent carries $5,500 a year, or $458 a month, before a dollar of principal.
Use the actual assessed value and the actual stacked rate for the specific parcel. A county average will mislead you by hundreds of dollars a month, and assessed value often resets toward the purchase price after a sale.
Hazard insurance, and what it excludes
The insurance line is annual premium divided by twelve. Premiums move with replacement cost, roof age, claims history, construction type and — increasingly — catastrophe exposure. Landlord policies generally cost more than owner-occupied ones and carry different liability structures.
Standard policies exclude flood. If the property sits in a mapped flood zone, a separate policy is required and can rival the primary premium. This calculator does not model flood, and neither do most quotes you will see early in a transaction.
Mortgage insurance: when it starts and when it stops
Conventional lenders generally require mortgage insurance when the loan exceeds eighty percent of value — a down payment under twenty percent. It is charged as an annual percentage of the loan balance, typically 0.3 to 1.2 percent, scaled by credit score and loan-to-value.
Two thresholds end it. Under the Homeowners Protection Act it cancels automatically once the balance reaches seventy-eight percent of the original value on schedule, and you can generally request cancellation at eighty percent. Both are computed from original value, not current market value, unless you order a new appraisal and your servicer accepts it.
This calculator flags the crossing automatically: push the down payment below twenty percent and it enables mortgage insurance and tells you the LTV.
Escrow: why the payment changes
Most lenders escrow taxes and insurance, collecting one twelfth each month and paying the bills when due. When either rises, the servicer performs an escrow analysis and adjusts the payment — usually upward, and usually with a lump-sum shortage spread across the following year.
This is the single most common reason a payment that was budgeted precisely at closing is wrong eighteen months later. Nothing about the loan changed. The assessment and the premium did.
What PITI leaves out
PITI is a housing payment, not a cost of ownership. It excludes maintenance, capital expenditure, association dues, flood insurance, closing costs and — for a rental — vacancy, management and turnover.
For a primary residence, PITI plus a maintenance reserve is a reasonable budget. For a rental, PITI is the starting line: see the DSCR page for what has to be subtracted before the number means anything.
Common questions
What does PITI stand for?
Principal, interest, taxes and insurance — the four components of a full monthly housing payment. Adding association dues makes it PITIA. Lenders underwrite the combined figure, not principal and interest alone.
When is private mortgage insurance required?
Conventional lenders generally require mortgage insurance when the loan exceeds eighty percent of the property value, meaning a down payment under twenty percent. It usually falls off automatically once the balance reaches seventy-eight percent of the original value, and can often be cancelled by request at eighty percent.
Does a larger down payment always reduce the monthly payment?
Yes for principal and interest, because you borrow less, and it can also remove mortgage insurance once you pass twenty percent. It does not change property tax or hazard insurance, which follow the property value rather than the loan. The trade-off is that capital parked in the property is unavailable for the next acquisition.
Why did my mortgage payment go up on a fixed-rate loan?
The principal and interest portion did not change. Escrowed property tax or insurance did. When an assessment or premium rises, the servicer re-analyses the escrow account and raises the monthly collection, often adding a shortage repayment spread over the following twelve months.