The single most expensive mistake in home buying isn't overpaying for the house — it's overestimating what you can afford. Lenders qualify borrowers up to 43–50% debt-to-income ratios; households that stretch there routinely feel house-poor within a year. The safer framework is the one most financial planners use: the 28/36 rule.
The 28/36 rule, in plain numbers
- 28% front-end: total housing costs — mortgage principal & interest, property taxes, insurance, any HOA — stay under 28% of gross monthly income.
- 36% back-end: all monthly debt combined (housing + car + student loans + card minimums) stays under 36%.
Example: $100,000 salary = $8,333 gross monthly. Your ceiling is about $2,333/month for all housing costs — and remember that's taxes, insurance, and maintenance too, not just the loan payment. HUD uses a similar 30% threshold to define "cost-burdened" households, which tells you how real this line is.
Down payments: how much is enough?
| Down payment | On a $400,000 home | Trade-off |
|---|---|---|
| 3–5% (program minimums) | $12,000–$20,000 | PMI required; biggest loan; easiest entry |
| 10% | $40,000 | Still PMI, smaller than at 5% |
| 20% | $80,000 | No PMI; best rates; strongest offers |
PMI (private mortgage insurance) typically runs 0.40%–1.50% of the loan per year — often hundreds of dollars monthly — until you reach 20% equity. On a $400K home, saving $80,000 over five years means putting away roughly $1,333 per month; a dedicated high-yield account shortens the timeline meaningfully (same automation principles apply).
Your credit score is money
Mortgage pricing is brutally credit-sensitive. Borrowers around 740+ get the best rates; a 620 score has recently averaged nearly a full percentage point higher. On a $350,000 loan, that gap costs tens of thousands over a 30-year term. If buying is 6–18 months away, spend that window on our credit-score playbook: on-time payments, sub-10% utilization, disputed errors removed.
First-time buyer programs worth checking
- Low-down-payment mortgages: conventional loans from 3–5% down for qualifying buyers; FHA from 3.5%.
- Lender programs: offerings like Chase's DreaMaker (3% down, up to $5,000 grant in select areas) or Rocket's ONE+ (lender contributes 2% toward down payment) target moderate-income buyers.
- State & local assistance: most states run down-payment-assistance programs via housing finance agencies — often forgivable grants or deferred loans.
A sane buying sequence
- Twelve-plus months out: build credit, pay down debts, automate the house fund into a HYSA (never stocks — your timeline is fixed).
- Six months out: know your 28/36 number cold; get pre-qualified to test it against local prices.
- House hunting: shop total monthly cost, not list price — taxes and insurance vary wildly by ZIP code.
- Offer time: get pre-approved (stronger than pre-qualification), compare loan estimates from at least three lenders.
- Before closing: re-verify nothing new hits your credit — no car purchases, no new cards mid-escrow.