How Much House Can You Really Afford? (The Bank's Answer Is Almost Always Too High)
Sarah and Ben got pre-approved for a $540,000 mortgage. They were thrilled. The bank said yes, the numbers worked on paper, and they bought a $510,000 house in suburban Chicago in early 2023. They stretched every penny for the 10% down payment and moved in feeling like they'd made it.
By 2024, they were quietly panicking. Property taxes: $9,200 a year — about $767 a month. HOA: $180 a month. A new furnace in January: $4,800. Two stable incomes, and they were living paycheck to paycheck in a house a major lender said they could easily afford.
The 28/36 rule — the formula banks use to decide how much mortgage you qualify for — is a minimum standard designed to protect lenders, not buyers. It tells you the maximum a lender will give you. That is a very different thing from how much house you can comfortably afford.
This guide is about finding that second number — the one that lets you live in your home without dreading the next appliance breakdown. Use the Home Affordability Calculator alongside it to get your own figures instantly.
⚠️ Disclaimer
This article is for informational purposes only and does not constitute financial or mortgage advice. Always consult a qualified mortgage professional or financial adviser before making home purchase decisions.
What Is the 28/36 Rule — and Why Do Banks Use It?
The 28/36 rule is a mortgage qualification guideline used by most US lenders, stating that housing costs should not exceed 28% of gross monthly income, and total debt payments should not exceed 36%. It was established by Fannie Mae and Freddie Mac — the government-sponsored entities that back most US mortgages — as a benchmark for loan eligibility, not for financial wellbeing.
The two thresholds break down like this:
| Ratio | Maximum | What It Covers |
|---|---|---|
| Front-end (28%) | 28% of gross monthly income | Mortgage, property tax, homeowner's insurance |
| Back-end (36%) | 36% of gross monthly income | All of the above + car loans, student loans, credit cards |
For a household earning $8,000/month gross:
- Maximum front-end payment: $8,000 × 28% = $2,240/month
- Maximum back-end debt: $8,000 × 36% = $2,880/month
FHA loans (common with first-time buyers) allow slightly higher ratios — 31% front-end and 43% back-end — which is why FHA pre-approval amounts often look more generous than conventional loan offers.
The Home Affordability Calculator runs both ratios automatically. Enter your gross income, monthly debts, interest rate, and down payment — it shows your qualification amount and a more conservative comfortable-purchase range side by side.
Why the Bank's Number Is Not Your Number
Here is the core problem: gross income and take-home income are very different things. If you earn $8,000/month gross, you might actually deposit $5,600–$6,000 after federal taxes, state taxes, health insurance, and retirement contributions.
But the 28/36 rule is calculated on your gross income. So when a bank says your housing payment can go up to $2,240/month, they mean 28% of $8,000 — not 28% of what actually lands in your bank account.
$2,240 ÷ $5,800 (estimated take-home) = 38.6% of your actual monthly income.
That gap is where people get into trouble. The bank is not lying — the formula is correct as written. But using gross income as the baseline inflates what "28%" means in real spending terms, because your taxes are not a choice you can trade off against your mortgage.
Key Takeaway
The 28/36 rule is a lender's minimum qualification standard, not a spending recommendation. It's calculated on gross income — before tax. Many financial planners use a tighter rule: keep your mortgage payment at or below 25% of your net (take-home) monthly income. That's the number that leaves room for real life.
How to Calculate Your Real Home Affordability
A more honest affordability formula uses your take-home pay — not your salary:
Worked example (US): Nadia earns $95,000/year. After federal income tax, state tax, health insurance, and 6% 401k contribution, her take-home is approximately $5,600/month.
- Max comfortable monthly payment (25% rule): $5,600 × 25% = $1,400/month
- At a 6.8% rate on a 30-year fixed mortgage, this supports a loan of approximately $213,000
- With a 10% down payment: maximum comfortable purchase price is around $237,000
Her bank pre-approved her for $370,000. The gap — over $130,000 — represents the financial cushion between qualifying and thriving.
Worked example (UK): Marcus earns £54,000/year in Manchester. After income tax and National Insurance, his take-home is approximately £3,250/month.
- Max comfortable monthly payment: £3,250 × 25% = £812/month
- At a 5.0% rate on a 25-year repayment mortgage, this supports a mortgage of approximately £147,000
- With a 15% deposit: he can comfortably buy up to around £173,000
UK lenders typically use income multiples (3.5–4.5× salary) rather than the 28/36 rule. At 4× income, Marcus would be approved for £216,000 — significantly more than the £147,000 the 25% take-home rule suggests. The difference is not what he qualifies for — it's what his monthly budget can actually sustain.
For Australian buyers, the comparable tool is the Home Affordability Calculator, which supports AUD inputs and accounts for the serviceability buffer (APRA mandates lenders assess affordability at 3% above the actual loan rate).
The Hidden Costs Banks Don't Count
The mortgage payment is just the starting point. Experienced homeowners know the full monthly cost of ownership includes several items that frequently catch first-time buyers off guard:
| Cost | Typical Annual Amount | Monthly Equivalent |
|---|---|---|
| Property tax (US average) | 0.5–2.2% of home value | $100–$550 on $300k home |
| Homeowner's insurance | $1,200–$2,400/year | $100–$200 |
| HOA fees (if applicable) | Varies widely | $50–$500+ |
| Maintenance and repairs | 1% of home value/year | ~$250 on $300k home |
| PMI (if <20% down) | 0.5–1.5% of loan/year | Varies |
On a $350,000 home, the non-mortgage monthly costs alone can easily add $800–$1,100:
- Property tax at 1.5%: $438/month
- Insurance: $150/month
- Maintenance reserve (1% rule): $292/month
Add that to a $1,850 mortgage payment and the real monthly cost is approximately $2,730 — not $1,850. The difference of $880/month, annualised, is over $10,000 a year the pre-approval estimate never mentioned.
💡 Pro Tip: The 1% Maintenance Rule
Set aside 1% of your home's purchase price annually for maintenance and repairs. On a $350,000 home, that's $3,500/year — or about $292/month sitting in a dedicated savings account. Homes built before 1990 or with older systems (roof, HVAC, plumbing) often need closer to 1.5–2%. This reserve prevents a single repair from derailing your finances.
Before you make an offer, look up the actual property tax on any home you're seriously considering — it's public record and searchable on most county assessor websites in the US. In the UK, check the council tax band for the property (Bands A–H). These are exact numbers, not estimates, and they can vary dramatically even between neighbouring streets.
What Mortgage Rate Does to Your Buying Power
Interest rate is the single biggest lever on home affordability. A 1-percentage-point change in rate shifts your purchasing power by roughly 10–12% — meaning the same monthly budget buys you significantly less house at higher rates.
| Rate | Monthly Payment on $300k (30yr) | Home Price at $1,500/month Budget |
|---|---|---|
| 4.0% | $1,432 | ~$314,000 |
| 5.0% | $1,610 | ~$279,000 |
| 6.0% | $1,799 | ~$250,000 |
| 6.8% | $1,961 | ~$230,000 |
| 7.5% | $2,098 | ~$215,000 |
At 7.5% versus 4.0%, the same $1,500 monthly budget buys almost $100,000 less house. This is why so many buyers who held out during the low-rate era of 2020–2021 feel priced out even in markets where sale prices haven't moved dramatically — because their purchasing power moved.
If you're weighing buying now versus waiting for rates to fall, the Rent vs Buy Calculator factors in rate assumptions, expected home price appreciation, and the opportunity cost of your down payment sitting in a savings account versus equity. It gives a more honest answer than "rent is throwing money away" (it's often not).
For buyers already carrying significant car payments or student loans, running the Debt Payoff Calculator first can show whether eliminating one debt substantially improves your back-end ratio — and therefore your mortgage options.
Frequently Asked Questions
What is a safe rule of thumb for home affordability?
Keep your total monthly housing payment — mortgage principal and interest, property tax, and insurance — at or below 25% of your net (take-home) monthly pay. This is more conservative than the lender's standard of 28% of gross income, but it leaves meaningful room for savings, emergencies, and life. Many certified financial planners use this as the true upper limit for comfortable ownership.
How much down payment do I actually need?
As little as 3% (conventional loan) or 3.5% (FHA). But 20% eliminates private mortgage insurance (PMI), which typically adds 0.5–1.5% of your loan value annually — roughly $1,500–$4,500/year on a $300,000 loan. If you can reach 20% without draining your emergency fund, the PMI savings are real. But waiting years to save it often costs more in rising prices and rent paid than PMI would have totalled.
Should I buy at the top of my pre-approval?
Almost never. A pre-approval ceiling is what you qualify for based on minimum lending standards — it is not a recommendation of what to spend. A useful stress test: imagine one income source disappearing (a partner's job, a client, a side income). Could you still make the mortgage payment? If the answer is no, you are probably at the top of what you should borrow, not what you should spend.
Does the 28/36 rule apply in the UK and Australia?
Not directly. UK lenders typically use income multiples — usually 3.5 to 4.5 times your annual salary — and stress-test affordability at a higher interest rate than the actual mortgage rate. In Australia, APRA mandates lenders assess affordability at 3% above the actual loan rate (the "serviceability buffer"). The underlying principle is the same — income-based limits — but the mechanics differ. The Home Affordability Calculator handles AUD and GBP inputs with country-appropriate calculation methods.
What about stamp duty, closing costs, and other buying fees?
These are separate from affordability but critical to budget for. In the US, closing costs typically run 2–5% of the purchase price. In the UK, Stamp Duty Land Tax applies above £250,000 for most buyers (check the Stamp Duty Calculator for the current rates). In Australia, stamp duty varies by state and can be 4–5% of the purchase price. These costs must come from savings on top of your down payment — they cannot be rolled into a standard mortgage.
Try It Yourself
The bank's pre-approval answers "how much will we lend you?" Your real question is "how much can I borrow and still afford to live?" — and those numbers are usually quite different.
Use the Home Affordability Calculator to find your number: enter your income, existing debts, down payment, and expected interest rate, and see both the lender's qualification amount and a more conservative comfortable-purchase range.
Also worth running:
- Rent vs Buy Calculator — is buying actually cheaper than renting over your time horizon?
- Amortization Calculator — see exactly how much of each payment goes to interest vs principal across your full loan term
- Debt Payoff Calculator — paying off existing debts first can significantly change what you're approved to borrow
