How the Mortgage Affordability Calculator Works
This calculator uses the 28/36 rule, a widely accepted guideline that lenders use to determine how much mortgage you can qualify for. The front-end ratio (28%) limits your total housing costs -- including principal, interest, property taxes, and insurance -- to no more than 28% of your gross monthly income. The back-end ratio (36%) limits your total monthly debt payments, including housing and all other debts, to 36% of gross income.
The calculator iteratively solves for the maximum home price by finding the largest loan amount whose monthly principal and interest payment, combined with estimated taxes and insurance, stays within both DTI limits. The more restrictive of the two rules determines your maximum affordability.
Keep in mind that this is a guideline, not a hard rule. Some lenders allow DTI ratios up to 43% or higher with compensating factors like excellent credit, large cash reserves, or a substantial down payment. FHA loans, for example, may allow up to 50% back-end DTI in certain cases.
Factors like HOA fees, PMI (if your down payment is below 20%), and local cost variations can further affect what you can truly afford. Always leave a financial cushion for unexpected expenses like repairs, maintenance, and property assessments.
Frequently Asked Questions
What is the 28/36 rule for mortgages?
The 28/36 rule states that your housing costs should not exceed 28% of your gross monthly income (front-end ratio), and your total debt payments should not exceed 36% (back-end ratio). Lenders use these guidelines to determine your maximum mortgage qualification.
Does this calculator include PMI?
This calculator does not include PMI (Private Mortgage Insurance). If your down payment is less than 20%, you will likely need to pay PMI, which typically costs 0.5% to 1% of the loan amount annually. This would reduce the home price you can afford.
What income should I use for the calculation?
Use your gross annual income before taxes and deductions. If you are applying with a co-borrower, combine both gross incomes. Include regular income sources like salary, bonuses (if consistent), and other documented recurring income.
Why do lenders use gross income instead of net income?
Lenders use gross income because tax situations vary widely between borrowers. Gross income provides a standardized measure for comparison. However, for personal budgeting, it is wise to consider your affordability based on take-home pay.
Can I afford more than what this calculator shows?
Possibly. Some loan programs allow higher DTI ratios, up to 43% or even 50% for FHA loans with strong compensating factors. However, just because you qualify for a higher amount does not mean it is financially comfortable. Many financial advisors recommend keeping housing costs well below the 28% threshold.