Before you start touring homes, you need a number — not a vague range, but an actual ceiling on what you can responsibly spend. Without it, it's easy to fall in love with a house that stretches your budget dangerously thin.

Lenders use a rule called the 28/36 rule to evaluate your application, and understanding it gives you a reliable anchor before you ever talk to a bank.

What the 28/36 Rule Is

The 28/36 rule sets two limits based on your gross (pre-tax) monthly income:

  • 28% front-end ratio: Your total monthly housing costs — mortgage principal, interest, property taxes, homeowner's insurance, and HOA fees if applicable — should not exceed 28% of your gross monthly income.
  • 36% back-end ratio: Your total monthly debt payments — housing costs plus car loans, student loans, credit cards, and any other recurring debt — should not exceed 36% of your gross monthly income.

Both limits must be satisfied. If your housing costs are under 28% but your total debt pushes you past 36%, lenders will flag that.

A Real-Numbers Example

Suppose your household earns $90,000 per year, or $7,500 per month gross.

  • 28% of $7,500 = $2,100/month maximum for housing costs
  • 36% of $7,500 = $2,700/month maximum for all debt payments

If you have a $400/month car payment and $300/month in student loan payments, that's $700 already going to debt. Your maximum housing payment drops to $2,000/month ($2,700 − $700), even though the front-end limit says $2,100.

The back-end ratio wins. Always calculate both. The binding constraint is whichever limit leaves you less room — and for buyers with existing debts, it's almost always the back-end ratio.

How to Translate a Monthly Payment to a Purchase Price

Once you know your maximum monthly housing cost, you can work backwards to a purchase price. Assume your payment of $2,000 needs to cover principal and interest, leaving roughly $400/month for taxes and insurance. That gives you about $1,600 for the actual mortgage payment.

At 7% interest on a 30-year mortgage, $1,600/month supports a loan of approximately $240,000. With a 20% down payment, that translates to a purchase price of around $300,000. With a 10% down payment, around $267,000.

FinWiser's free mortgage calculator lets you enter any purchase price and see the exact monthly payment — useful for testing different price points quickly.

Why 20% Down Still Matters

Putting less than 20% down triggers private mortgage insurance (PMI), which typically adds 0.5–1.5% of the loan amount to your annual costs. On a $280,000 loan, that's $1,400–$4,200 per year, or up to $350/month extra on top of your mortgage.

PMI doesn't build equity — it's pure insurance for the lender. It cancels automatically once your loan-to-value ratio hits 80%, but that can take years. If you're near the 20% threshold, it's often worth waiting a little longer to save the additional down payment.

What the Rule Doesn't Account For

The 28/36 rule is a lender's benchmark, not a personal financial plan. There are a few things it doesn't factor in:

  • Emergency fund: If buying the home wipes out your savings, you're one HVAC failure away from credit card debt. Most advisors recommend keeping 3–6 months of expenses liquid after closing.
  • Maintenance costs: Budget 1–2% of the home's value per year for repairs and upkeep. A $350,000 home could need $3,500–$7,000 in maintenance annually.
  • Future income changes: If one partner plans to stop working, if you're in a commission-based role, or if you're near retirement, the 28/36 limit at today's income may be too aggressive.

A More Conservative Starting Point

Many financial planners recommend targeting 25% or less of gross income for housing, not 28%. That buffer gives you room for savings, investing, and the unexpected without constantly feeling squeezed. If you can comfortably stay below 25%, you'll have more flexibility than most homeowners.

The 28/36 rule tells you the maximum a lender will typically approve. It doesn't tell you what will make you financially comfortable — that's a number only you can determine based on your lifestyle, goals, and risk tolerance.

Use FinWiser's free mortgage calculator to run your own numbers in seconds — enter your target home price, down payment, and rate to see your exact monthly payment and whether it fits within your 28% threshold.