The 28/36 Rule vs. the 2.5× Income Rule: Which to Trust
The 28/36 rule (housing costs under 28% of gross income, total debt under 36%) is the framework lenders actually use for approval. The 2–2.5× income rule is an older, blunter heuristic that ignores interest rates and existing debt entirely — it tends to be more conservative, but less precise to your actual situation.
Both rules show up constantly in home-buying advice, and both are legitimate — they just measure different things, which is why they can point to noticeably different home prices for the same household.
What each rule actually measures
The 28/36 rule is a debt-to-income framework: 28% of gross income for housing costs alone, 36% for housing plus all other debt combined. It's directly tied to actual lending practice and adjusts naturally for existing debt — someone with no car payment has more room under the 36% ceiling than someone with a $500 monthly car loan.
The 2 to 2.5× annual income rule is a flat multiplier applied to home price directly, with no adjustment for interest rate, existing debt, or down payment. It was more reliable in earlier eras of more stable interest rates, and it remains a useful conservative gut-check today, even though it's cruder than a DTI-based calculation.
Why they can disagree
At a low interest rate with no other debt, the 28/36 rule often supports a higher home price than the 2.5× rule would suggest — the DTI framework is more generous when rates are favorable. At a high interest rate or with significant existing debt, the two can converge or even flip, with the DTI-based number coming in lower than the flat multiplier.
Neither is universally "more correct" — the 28/36 rule better reflects what a lender will actually approve today; the 2.5× rule is a simpler, rate-independent sanity check that tends to keep people from over-extending regardless of current rate conditions.