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Mortgage Approval Estimate Basics (Without the Hype)

Housing and total DTI rules of thumb, why max home price is not a pre-approval, and how down payment, debts, APR, and taxes change the estimate.

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“How much house can I afford?” is usually a budget and debt-capacity question first, and a credit/underwriting question second. Online estimates only model the first part.

Housing DTI and total DTI

Housing DTI (front-end) compares housing costs to gross monthly income. A common planning rule of thumb is around 28% for principal, interest, taxes, insurance, and PMI when loan-to-value is high.

Total DTI (back-end) adds other monthly debts — car loans, student loans, credit card minimums, and similar — on top of housing. A classic paired rule of thumb is about 36% total when housing is 28%.

Some buyers stretch further — for example 33% / 40% or 36% / 43% housing and total DTI. Those are more aggressive planning assumptions, not a guarantee a lender will approve them. These percentages are not laws and not a promise of approval.

The mortgage approval estimate sizes the main result at a typical 28% housing / 36% total DTI. Expand the breakdown to compare max home price, loan, and housing budget at 33% and 36% housing DTI (with higher total DTI caps) as well. Enter other monthly debts so the back-end cap can shrink the housing budget when non-mortgage payments are large.

From payment budget to home price

Once a monthly housing budget is set (the tighter of front-end and back-end caps):

  1. Reserves room for annual property tax (entered in dollars, divided by 12) and annual insurance
  2. Estimates PMI when LTV is above 80% (from down-payment percent unless you override)
  3. Puts the rest into principal and interest at your annual interest rate (APR) and term (10, 15, or 30 year presets)
  4. Converts that P&I into a maximum loan
  5. Adds your down payment to get a rough max home price

Tax and insurance are fixed dollar inputs in this model, so they shrink the room left for principal and interest. High other debts can zero out room for a new mortgage even when income looks fine on paper.

Why this is not a pre-approval

A real lender also looks at:

  • Credit history and score
  • Employment and income documentation
  • Cash reserves after closing
  • Property appraisal and condition
  • Program rules (conventional, FHA, VA, etc.)

This site does not pull credit, contact lenders, or guarantee approval. See our Terms.

Practical tips

  • Stress-test a higher APR than today’s quote
  • Leave room for maintenance and utilities (not in housing DTI math)
  • Include realistic other monthly debts so total DTI is not understated
  • Run the mortgage payment calculator on a specific price to see P&I vs escrow

Try it yourself

Open the Mortgage Approval Estimate, enter income, down payment, other monthly debts, APR, and annual property tax, then open the breakdown to compare DTI scenarios — that is the tradeoff between a safer payment and stretching for more house in this model.