Calculator Panel
Calculation Ready
Enter your values above and click Calculate.
What This Calculator Does
This calculator reverse-engineers mortgage lending underwriting rules to estimate your maximum affordable loan size based on income, current debt payments, interest rate, and term.
How to Use This Calculator
Enter gross income, current debt, interest rate, term, and target DTI (defaults to 36%), then click Calculate.
How the Calculation Works
The underlying math engine processes your inputs using exact formulas. This systematic approach ensures professional, institutional-grade calculation precision:
Mathematical Formula
Formula Legend:
- · Gross Monthly Income = Your pre-tax monthly household earnings.
- · Target DTI = The maximum back-end Debt-to-Income ratio (typically 36% to 43%).
- · Current Monthly Debts = Existing recurring payments (car loans, credit card minimums, student loans).
Practical Example
Suppose your gross monthly income is $10,000, your current monthly debts total $600, you target a conservative 36% DTI, and mortgage rates are 6.5% for a 30-year term:
Step-by-Step Mathematical Walkthrough:
- 1 Calculate maximum total debt allowance: $10,000 * 0.36 = $3,600.
- 2 Subtract existing debts: $3,600 - $600 = $3,000 maximum monthly mortgage payment (Principal & Interest).
- 3 Solve for loan principal given $3,000 payment: approximately $474,626 mortgage capacity.
Important Assumptions & Notes
- No property tax, homeowner insurance, or PMI is included in the loan principal estimation.
- Lenders approve financing based on standard qualified mortgage parameters.
Common Mistakes or Considerations
- Borrowing the absolute maximum borrowing power, leaving no budget room for home maintenance, utilities, or emergency cash savings.
Frequently Asked Questions
What determines my borrowing power?
Your gross monthly income, existing debt obligations, credit score, and current mortgage interest rates are the primary factors.
What DTI percentage do lenders use to limit loans?
Most conservative mortgage programs use a 36% back-end DTI limit, though FHA loans and some conventional products can go up to 43% or 50% under strict conditions.
How do rising interest rates affect my borrowing power?
Rising interest rates decrease borrowing power. Because more of your monthly payment is consumed by interest, the total loan principal you can afford drops significantly.
Should I buy a home at my maximum borrowing capacity?
Typically no. This makes you 'house poor,' meaning almost your entire income is committed to mortgage payments, leaving no safety margin for life expenses.