What is the Mortgage Affordability Calculator?
This calculator checks whether a specific home purchase fits comfortably within your income by applying the same front-end and back-end debt-to-income ratios mortgage lenders use during underwriting. It also checks whether your available savings actually cover the down payment plus closing costs — a step many "can I afford it" estimates skip.
How does the underlying math work?
The calculator first computes the monthly principal-and-interest payment with the standard amortization formula used across the site's Mortgage Calculator, then adds estimated property tax, homeowners insurance and HOA dues to get your total monthly housing cost. The front-end ratio divides that housing cost by your gross monthly income; the back-end ratio (DTI) adds in your other monthly debt payments before dividing by income. A home is flagged as affordable when the front-end ratio stays at or under 28%, the back-end ratio stays at or under 36%, and your savings cover the down payment plus an estimated 3% of the price in closing costs.
Real-world practical application
Buyers use this before house-hunting to set a realistic price ceiling, before making an offer to sanity-check a listing against their own numbers (not just what a lender pre-approved), and to see how much a larger down payment or a shorter amortization period changes the monthly cost and the ratios. It's also a quick way to see whether a tempting price range is being driven more by income or by other existing debt.
Frequently Asked Questions
What is a good front-end and back-end debt-to-income ratio?
Lenders commonly use 28% as the comfortable ceiling for housing costs alone (front-end ratio) and 36% for total debt including housing (back-end ratio, or DTI). Many conventional loan programs will approve a DTI up to 43%, and some government-backed programs go higher, but staying under 36% leaves more breathing room.
Does this calculator check if I'll actually get approved for a mortgage?
No. It checks your numbers against the general guidelines lenders use, not a specific lender's underwriting rules, which also weigh credit score, employment history, assets and loan program. Treat the result as a sanity check before you apply, not a pre-approval.
Why do closing costs matter if I already have the down payment saved?
Closing costs — lender fees, title insurance, appraisal, taxes and more — typically run 2%-5% of the purchase price and are due on top of the down payment at closing. Savings that cover the down payment alone can still leave you short of the cash actually needed to close.
Related Calculators
- Mortgage Calculator — full year-by-year amortization for a given loan.
- Debt Snowball & Emergency Fund Calculator — clear other debt before taking on a mortgage.
- Rule of 72 — how fast a down-payment fund could grow while you save.