“How much house can I afford?” is the first question of every home search — and the one most often answered wrong. The trap is confusing two very different numbers: the maximum a lender will approve, and the amount you can comfortably live with. A bank might green-light a $2,300 monthly payment when the figure that lets you keep saving and sleep at night is closer to $1,800. The first is a ceiling. The second is where you actually want to be.
How lenders decide
Lenders work from your debt-to-income ratio — your monthly debt payments divided by your gross monthly income — and apply two limits:
| Ratio | What it covers | Typical cap |
|---|---|---|
| Front-end | Housing only (principal, interest, taxes, insurance) | ~28% of gross |
| Back-end | All debt (housing + car + cards + student loans) | ~43% of gross |
They take whichever limit produces the lower payment. Add your down payment to the loan that payment supports, and you have your maximum price. Our mortgage qualifier calculator runs exactly this, and the required-income calculator works it backward from a target home.
A full worked example
Let’s run a real household: $90,000 a year ($7,500/mo gross), with a $400 car payment and a $250 student loan.
| Step | Figure |
|---|---|
| Front-end limit (28% × $7,500) | $2,100 |
| Back-end limit (43% × $7,500 − $650 debt) | $2,575 |
| Housing budget (the lower) | $2,100 |
| − taxes & insurance (est.) | −$400 |
| = principal & interest budget | ~$1,700 |
| Loan that supports (≈6.5%) | ~$269,000 |
| + 20% down payment | + $67,000 |
| Maximum price | ≈ $336,000 |
That’s the lender’s ceiling. Whether you actually want to spend $2,100 a month on housing is the next, more important question.
Why the lender’s maximum isn’t your budget
Those ratios use gross income — before taxes, retirement contributions and health premiums come out. They also ignore the real costs of owning: maintenance, higher utilities, furnishing, and the life you want to keep funding. Borrow to the ceiling and you become “house poor” — a big asset and zero breathing room.
Qualifying for a mortgage tells you the maximum you can borrow. Your budget tells you the maximum you should. The gap between them is where financial stress lives.
A more conservative target many planners use: keep total housing costs under 25–28% of take-home (net) pay, and confirm you’re still saving 15%+ for retirement after the payment.
How interest rates reshape your budget
Because your payment is fixed by your budget, the rate decides how much house that payment buys. Here’s what the same $1,680 monthly principal-and-interest supports across rates:
| Rate | Loan it supports | vs. 5% |
|---|---|---|
| 5% | ~$313,000 | — |
| 6% | ~$280,000 | −$33,000 |
| 7% | ~$252,000 | −$61,000 |
| 8% | ~$229,000 | −$84,000 |
A single point of rate moves your buying power by tens of thousands — which is why locking a good rate matters as much as negotiating the price.
How your down payment changes everything
A bigger down payment shrinks the loan and, at 20%, removes PMI. On a $350,000 home at 6.5%:
| Down payment | Loan | PMI? | Est. monthly (P&I + PMI) |
|---|---|---|---|
| 5% ($17,500) | $332,500 | Yes | ~$2,300 |
| 10% ($35,000) | $315,000 | Yes | ~$2,170 |
| 20% ($70,000) | $280,000 | No | ~$1,770 |
Reaching 20% down cuts the monthly cost by roughly $500 here — but never drain your reserves to get there (see the stress test below).
The costs beyond the payment
The mortgage payment is only part of the picture. Budget for these too:
| Cost | Rule of thumb | On a $300,000 home |
|---|---|---|
| Property taxes + insurance | Often escrowed into the payment | varies by state |
| Closing costs | 2–5% of price, paid upfront | $6,000–$15,000 |
| Maintenance | ~1% of value per year | ~$3,000/yr |
Estimate the first two with the mortgage calculator with taxes and insurance and the home closing cost calculator.
The stress test before you sign
Before you commit to the top of your range, walk this list honestly:
- Could you make the payment on one income for a few months if you had to?
- Do you still have 3–6 months of expenses after the down payment and closing costs?
- Are you still saving 15%+ for retirement with the payment in place?
- Does the budget survive a surprise — a $3,000 repair, a rate reset on an ARM, a higher tax bill?
If any answer is “no,” step down a price tier. The house will still be a house; the breathing room is what you’ll actually live in.
Find your number
Start with what the lender allows, then pull it back to what fits your real, after-tax life. Run your income and debts through the mortgage qualifier, sanity-check the payment against your take-home pay with the mortgage calculator, and once you own it, pay it down faster. The complete mortgage guide puts affordability, down payment, PMI and closing costs into one plan.
