It isn't just principal and interest. Four things typically make up the payment: principal, interest, property taxes, homeowners insurance, and PMI where it applies.

Taxes and insurance are collected through an escrow account. Your lender sets aside a portion each month and pays those bills when they come due. You don't have to manage the invoices yourself, but the cost lands inside your monthly payment.

If the property sits in an HOA or condo association, dues are added on top. Those usually aren't escrowed and are paid separately, but underwriting still counts them as an obligation when qualifying you.

This is why the figure from an online calculator rarely matches what actually gets billed — most calculators compute principal and interest only. In markets with heavy property tax burdens, the gap runs into the hundreds of dollars a month. Bergen County, New Jersey and Fairfax and Loudoun County, Virginia are clear examples.

The amount also isn't fixed. Principal and interest stay the same, but taxes and insurance change annually, and your escrow adjusts accordingly — which changes your monthly payment. We establish the full payment picture for a specific property before you commit to it.