Methodology
Every number on this site comes from a public source and a formula you can check. Here they are.
The affordability calculation
Purchase price is solved so that principal, interest, property tax, homeowners insurance, HOA dues and mortgage insurance together consume exactly the target share of gross income — 33% by default, the sustainable middle rather than a lender’s maximum. Price is additionally capped at the program’s total debt-to-income ceiling: 45% for conventional, FHA and credit-union products, 41% for VA, which is the residual-income benchmark.
Principal and interest use the standard amortization formula over 360 months. Funding fees are financed into the loan, which is how nearly everyone pays them, so on zero-down programs the loan exceeds the purchase price. Cash to close adds about 2.5% of price for lender, title, escrow and prepaid items on top of any down payment; it excludes reserves, which lenders also want to see.
Where the data comes from
| Input | Source | Refresh |
|---|---|---|
| Home values | Zillow Home Value Index, county and city | Monthly |
| Property tax | Census ACS 5-year, median real-estate tax divided by median home value (tables B25103 and B25077) | Annual |
| Loan limits | FHFA conforming loan limits | Annual, each November |
| Mortgage rates | Freddie Mac PMMS weekly survey, no discount points | Weekly |
Where it is weakest
- Insurance is a statewide average, not a quote. It varies enormously with the age of the home, roof condition, and wildfire or flood exposure. This is the softest number on the site.
- Mortgage insurance defaults assume strong credit. Below a 700 score the rate can double.
- Property tax is a county-wide effective rate derived from medians, not your parcel’s actual assessment.
- Zillow re-estimates its entire history each month, so values shift slightly between refreshes. We do not claim point-in-time reproducibility.
- Take-home pay uses federal brackets and FICA with the standard deduction and no retirement contributions.
Rates are the biggest lever
A 70 basis point move in rates changes purchasing power by roughly 6%. The rates used here are no-points survey averages. A quote that includes discount points will look lower than it truly is — always compare on the same basis, and read the Loan Estimate rather than the advertisement.