Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
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What does this calculator estimate?
Mortgage affordability estimates how much home you can qualify for, based on your income, debt, down payment, rate, and other monthly housing costs. It uses the standard debt-to-income window lenders apply. Enter your income and debts to see your range.
- Front-end DTI cap ~28% of gross income
- Back-end DTI cap ~36% including all debts
- Total payment includes taxes, insurance, and HOA
How mortgage affordability works
Lenders cap your total monthly debt payments at a percentage of your gross monthly income — typically 28% for housing alone (front-end) and 36% for all debt (back-end). The calculator works backward from that cap to find the largest mortgage you can support.
Limitations to watch for
The calculator uses your inputs, but lenders apply stricter real-world rules (credit score, reserves, the actual tax/insurance rates) and a qualifying interest rate that can differ from the one you enter. DTI is a floor, not the full picture — you should also be comfortable with the payment, and remember property taxes and insurance can rise.
How to use it in practice
Use DTI as a self-check before you pre-qualify. A comfortable purchase usually keeps housing payment well under the 36% back-end cap, leaving room for lifestyle and savings. Budget for taxes, insurance, and HOA on top of the principal + interest, and get an exact rate quote from a lender.
- Enter your gross monthly income and monthly debts.
- Enter your down payment, rate, term, and tax/insurance/HOA costs.
- The calculator finds the mortgage size that keeps you within the DTI window.
How this calculator works
Formula
Affordable mortgage is solved by setting the monthly housing payment (principal + interest + property tax + insurance + HOA) against your gross monthly income and existing debts, using a target debt-to-income ratio (commonly 28% front-end, 36% back-end).
Worked example
A $90,000 gross annual income ($7,500/month), no debts, with a 6.5% rate, 30-year term, 20% down, and $350/month taxes+insurance, supports roughly a $400,000 purchase at a 36% back-end DTI.
Assumptions to verify
- The target DTI (28% front-end / 36% back-end) is a standard guideline, not a guarantee.
- Property tax, insurance, and HOA are included in the monthly payment.
- The result is an estimate, not a pre-approval — a lender sets the final number.
Frequently asked questions
How much house can I afford?
A common guideline keeps your total housing payment at or under 28% of gross income, and all debts under 36%. The calculator applies this to your income.
What is the 28/36 rule?
The 28% front-end (housing only) and 36% back-end (all debt) DTI benchmarks many lenders use as a cap.
Does the payment include taxes and insurance?
Yes — a true housing payment includes principal, interest, property tax, and insurance (plus HOA if applicable). The calculator uses the full figure.
What counts toward DTI?
Gross monthly income in the denominator; the housing payment and all other minimum debt payments in the numerator.
Can I afford more than DTI says?
Often, but a lender may not approve it, and living at the DTI ceiling leaves little room for savings or unexpected costs. Aim for comfort, not the max.
Should I get pre-approved?
Yes — a real pre-approval from a lender gives the exact qualifying number and rate, far more accurate than an estimate.
How does the down payment affect it?
A bigger down payment reduces the loan amount and monthly payment, and can also avoid private mortgage insurance (below 20% typically adds PMI).
Cite this tool
BoringToolsKit. “Mortgage Affordability Calculator.” boringtoolskit.com/mortgage-afford/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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