Why the 28% rule misleads

The 28% rule says your housing payment shouldn't exceed 28% of gross monthly income (the fuller "28/36" version adds a 36% cap on total debt payments). It dates to mid-century mortgage underwriting, and it survives because it's easy: one division, one comparison, done. Lenders still use versions of it to decide what they'll lend. The mistake is treating it as an answer to what you can afford — those are different questions, and the gap between them is where plans quietly break.

The rule grades a payment. You're buying a future.

Consider two households, each earning $180,000 and eyeing the same $650,000 house. Same price, same rate, same payment — the 28% rule scores them identically. But the first household spends $4,500 a month outside housing, has $300,000 already invested, and wants the option to stop working at 60. The second spends $8,000 a month, has $40,000 saved, and wants the same thing. The rule cannot tell these situations apart, because the rule never asks what the money that isn't the payment is supposed to be doing. For most people the honest answer is: becoming the portfolio you'll eventually live on.

That's the reframe this site is built on. A house is affordable if, after carrying it, your remaining cash flow still compounds into financial independence on your timeline — with realistic odds, not in a best-case spreadsheet. Ask it that way and affordability stops being a ratio and becomes a probability.

Four things the ratio can't see

The full cost of owning. The 28% rule is usually applied to principal-interest-taxes-insurance. Maintenance (roughly 1% of home value a year, forever), HOA dues, PMI under 20% down, and the 5–6% cost of eventually selling are all real, and all invisible to the ratio. On a $650,000 home, maintenance alone is another ~$540 a month that behaves exactly like a payment.

Taxes. Two identical salaries keep different amounts in California and Texas — a gap that compounds for thirty years. The ratio is computed on gross income, so it never notices. State by state, the same household's odds move by whole percentage points.

Risk that arrives correlated. Layoffs cluster in the same years markets fall. A payment that's comfortable on your current salary can become a forced sale when six months of income disappear into a 30%-down market and the down payment already drained your buffer. A ratio checked once, on the day you buy, has no opinion about any of this; a simulation that draws thousands of futures — including the ugly ones — does.

Your timeline. "Affordable" at 28% can still mean retiring at 70 instead of 58. Only a model that tracks your portfolio against a target can price the thing you're actually giving up.

What to use instead

Not a stricter ratio — a different question. For any candidate price, ask: across thousands of simulated futures with crashes, layoffs, real taxes, and the full cost of owning, what fraction still reach my number by my target age? That's computable in your browser in about a second. See the concrete version for combinations like a $500K house on a $150K salary, or run your own numbers — the price where your odds turn from comfortable to risky is usually a much more interesting number than 28% of anything.

Why the 28% rule misleads

The rule grades a payment. You're buying a future.

Four things the ratio can't see

What to use instead

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