The 28/36 rule behind the number
Most conventional lenders evaluate two ratios. The front-end ratio caps total housing costs at about 28% of your gross monthly income, and the back-end ratio caps all recurring debt — housing plus car loans, student loans, and credit card minimums — at roughly 36%. Whichever limit is more restrictive for your situation becomes your true ceiling. If you carry significant other debt, the 36% back-end rule will bind before the housing rule does.
Lenders use gross (pre-tax) income, but your budget lives on take-home pay. A payment that qualifies on paper can still feel tight after taxes, retirement contributions, and everyday expenses. Many financial planners suggest targeting 25% or less of gross income for housing to leave room for saving and emergencies, especially in a high-rate environment.
Beyond the mortgage: the hidden costs of ownership
The maximum price this tool shows reflects the loan you can qualify for, not the full cost of owning. Budget an additional 1–2% of the home's value each year for maintenance and repairs, plus property taxes, insurance, and any HOA dues. On a $400,000 home, that maintenance reserve alone is $4,000–$8,000 annually.
A practical strategy is to buy at 80–90% of your calculated maximum. That margin absorbs rate changes, unexpected repairs, and life events without pushing your finances to the edge. The goal is a home you can enjoy, not one that consumes every spare dollar.