Can I Afford to Buy a House? The Honest Calculation Most Buyers Skip

I approved a mortgage for a couple last month who couldn’t actually afford it. The bank said yes. Their budget said no. This happens constantly, and it’s why I’m writing this today.

Most buyers focus on one number: the monthly payment. That’s dangerously incomplete. Banks use a formula. You need to use it too—then go further.

The Real Affordability Formula Banks Use (And Why It’s Not Enough)

Lenders rely on two debt-to-income ratios.

Front-end DTI caps your housing payment at 28% of gross monthly income—principal, interest, taxes, and insurance combined. On $6,000 monthly income, your max is $1,680.

Back-end DTI limits total debt to 36-43% of gross income. That same $6,000 income allows $2,160-$2,580 total monthly obligations—including your mortgage, car loans, credit cards, and student loans.

Here’s what lenders don’t emphasize: you can hit both limits simultaneously. A client earning $84,000 annually had a front-end limit of $1,960 per month. But $620 in student loans consumed back-end capacity. Their real max mortgage payment was $1,340. That difference cost them $80,000 in purchasing power.

Banks prioritize their risk, not your financial security. You need a stricter standard than they do.

The Hidden Costs Buyers Always Forget

You’ve calculated your mortgage payment. Most buyers stop there. Here’s what they miss on a $350,000 purchase:

Closing costs: 2-5% of purchase price. Average $12,250 due at closing—cash, not financed.
Property taxes: 0.8% annually in a low-tax state, up to 2.2% in New Jersey. On a $350,000 home in NJ, that’s $640 monthly.
Homeowners insurance: $100-$200 monthly depending on location and home age.
HOA fees: $200-$500+ monthly in many communities. Mandatory. Non-negotiable.
Maintenance reserve: 1-2% of home value annually. A $350,000 home needs $3,500-$7,000 set aside each year for repairs and replacements.

Add it up: beyond the mortgage, you’re looking at $1,200-$1,800 per month in carrying costs on a $350,000 home. Most buyers never plan for this. Then the furnace dies and they’re in crisis.

The Income You Actually Need at Each Price Point

Working backward from real numbers (20% down, 7% rate, 30-year term, 0.8% property tax):

$250,000 home: Mortgage $1,197 + tax $167 + insurance $125 + maintenance $208 = $1,697/month total. Required gross income: $72,720/year.

$350,000 home: Mortgage $1,677 + tax $233 + insurance $140 + maintenance $292 = $2,342/month total. Required gross income: $100,380/year.

$500,000 home: Mortgage $2,395 + tax $333 + insurance $180 + maintenance $417 = $3,325/month total. Required gross income: $142,500/year.

These assume zero other debt and no HOA. Add student loans or a car payment and the required income jumps another $15,000-$25,000 per year.

What Banks Approve vs. What You Can Actually Afford

The gap here is dangerous. A couple earning $95,000 combined came to me pre-approved for $320,000. Their actual picture: $420/month in student loans, $380/month car payment—$800 in existing debt.

At 36% back-end DTI, their total debt ceiling was $2,850/month. Subtract $800 existing, and they had $2,050 for a mortgage. That covers roughly a $280,000 loan. With their 15% down payment, their comfortable purchase price was $329,500.

The lender approved a $376,000 purchase. At $2,420/month, they’d have no emergency buffer, no savings, no retirement contributions beyond the minimum. At $2,050/month, they’re comfortable.

Use this rule: your bank approval is your maximum. Your actual comfortable budget is 20-30% lower. Buy at the lower number.

When Renting Is Still the Right Answer

The homeownership break-even point typically arrives after 5-7 years. Before that, renting often costs less once you factor in closing costs, maintenance, and the opportunity cost of your down payment sitting in a home instead of invested.

Renting is smarter right now if: you’ll move within 3 years, your back-end DTI exceeds 45% after a mortgage, your emergency fund would drop below 3 months of expenses after closing costs, or you’re in a market where prices are declining year over year.

None of these are permanent. They’re timing issues. Fix them in 12-18 months and buy then.

Your 5-step self-assessment today: (1) Calculate your back-end DTI including all debts. (2) Identify the full monthly cost of the home—not just the mortgage. (3) Confirm you’ll have 3 months emergency fund after closing. (4) Check you’re planning to stay 5+ years. (5) If all four pass, get pre-qualified. If any fail, set a specific date to fix them and revisit.

Buying a home you cannot truly afford is the most expensive financial mistake most people make. Run the real numbers first.