The quickest rule of thumb lenders and financial educators have used for decades is the 28/36 rule: spend no more than 28% of your gross monthly income on housing, and no more than 36% on all your debt payments combined. On a $6,000 a month gross income, that works out to roughly $1,680 for housing and $2,160 for housing plus every other loan payment you carry.
That is a starting point, not an answer. The 28/36 rule is a screening test built around ratios, and it says nothing about your childcare bill, your commute, your job security, or how much you want left over at the end of the month. Two households with identical incomes can have wildly different comfortable budgets. Treat the rule as the outer edge of the sensible range — then work backwards from your actual spending to find the number you can live with.
What the 28/36 rule actually says
The rule splits into two ratios, both calculated on gross (pre-tax) monthly income:
- The front-end ratio (28%) — your total monthly housing payment divided by gross monthly income.
- The back-end ratio (36%) — your housing payment plus car loans, student loans, personal loans, and minimum credit-card payments, divided by gross monthly income.
Here is a worked example. Suppose a household earns $6,000 a month gross, pays $300 on a car loan and $150 on a student loan. All figures below are illustrative arithmetic, not a quote or an approval.
| Step | Calculation | Result |
|---|---|---|
| Gross monthly income | — | $6,000 |
| Front-end cap (28%) | $6,000 × 0.28 | $1,680 for housing |
| Back-end cap (36%) | $6,000 × 0.36 | $2,160 for all debt |
| Existing debt payments | $300 car + $150 student loan | $450 |
| Housing allowed by back-end test | $2,160 − $450 | $1,710 |
| Governing limit | lower of $1,680 and $1,710 | $1,680 per month |
Notice what happens if that car payment were $700 rather than $300: the back-end test would allow only $1,310 for housing, and the car, not the house, would be setting the budget. Clearing short-term debt before you apply is often the fastest way to raise the number a lender will work with.
What "housing cost" really includes
This is where first-time buyers most often go wrong. The $1,680 in the example above is not the loan payment. It is the whole cost of occupying the home, and lenders generally measure it as PITI — principal, interest, taxes and insurance — plus association dues where they apply.
- Principal and interest — the loan repayment itself, the only part most affordability estimates in your head account for.
- Property tax — set locally, varies enormously between states and even neighbouring districts, usually collected monthly into escrow, and liable to be reassessed after you buy.
- Homeowners insurance — required by every lender, and priced on the property, not just on you. Flood, wind or earthquake cover may be separate and additional.
- HOA or condo fees — not part of your loan, but counted in your housing ratio, and they can rise or be supplemented by special assessments.
- Mortgage insurance — typically required with a conventional down payment under 20% (PMI), and structured differently again on FHA, VA and USDA loans.
- Maintenance — not counted by any lender, but very real. Roofs, water heaters and HVAC systems fail on their own schedule.
Stack these up and the loan payment might be only two-thirds of what leaves your account each month. If the illustrative $1,680 budget has to absorb, say, $300 of tax and insurance escrow and $80 of association dues, only about $1,300 is left for principal and interest — a meaningfully smaller house than $1,680 would buy. Our property tax estimator lets you sanity-check that escrow line separately before you combine it with the rest.
What a lender approves vs. what you can comfortably afford
Underwriting is not the same exercise as budgeting. A lender is assessing the probability that you repay them; you are deciding what kind of life you want to fund alongside the mortgage. Lenders weigh four things in particular:
- Debt-to-income ratio. The 28/36 rule descends from this, but real programmes are more flexible. Many loans are written above a 36% back-end ratio when other factors are strong, and different programmes apply different ceilings. Guidelines also change over time.
- Credit history. Your score influences both whether you qualify and the rate you are offered — and the rate feeds straight back into how much house the same payment buys.
- Down payment. A larger deposit shrinks the loan, can remove mortgage insurance, and often improves pricing. It is also the lever most buyers have the clearest control over.
- Reserves and stability. Savings left after closing, plus a consistent, documentable income history, both reduce perceived risk.
Because those factors can push an approval well past 36%, the number on your pre-approval letter is frequently higher than the number you should spend. The approval tells you the ceiling. Your own cash-flow arithmetic — after tax, after retirement contributions, after childcare, after the things that make life tolerable — tells you the floor you would regret crossing. Where those two disagree, trust your own.
How interest rates change your buying power
Affordability is expressed as a monthly payment, but a house is priced as a lump sum, and the rate is what converts between the two. Small rate moves have surprisingly large effects on the price you can reach.
Take the $1,300 of principal and interest from the example above on a 30-year loan. At a hypothetical 5% rate, that payment supports a loan of roughly $242,000. At a hypothetical 7%, the same $1,300 supports only about $195,000 — near enough a fifth less house for exactly the same monthly outlay. Those two rates are chosen purely to show the mechanics; they are not a forecast, a market observation, or a quote, and the rate you are actually offered depends on your credit, loan type, term, points and the day you lock.
So shop several lenders, because pricing genuinely differs, and re-run your numbers if rates move while you are searching. Be wary, too, of stretching to the top of your budget on the assumption you will refinance later — refinancing depends on future rates and future underwriting, neither of which is promised to anyone.
The hidden costs of buying
The monthly payment is only half the affordability question. The other half is the cash you need on the day and in the months immediately afterwards.
- Closing costs. Lender fees, appraisal, title work, recording, prepaid taxes and insurance, and escrow funding — a substantial sum on top of the down payment. Amounts vary widely by state, loan and lender; our closing cost calculator helps you size the range.
- Moving. Movers, deposits, utility connections and time off work.
- Immediate repairs. Inspections routinely surface work that cannot wait — electrical faults, roof patches, a failing water heater.
- Furnishing and equipping. Appliances, tools, curtains, and a lawnmower you never previously owned.
- An untouched emergency fund. Arriving at closing with savings at zero is the most common way an affordable-on-paper purchase becomes a stressful one.
Put your own numbers in
Rules of thumb get you to a shortlist; arithmetic gets you to a decision. Start with our mortgage calculator to see how a given price, deposit, term and rate translate into a monthly payment, then adjust the rate up and down to see how sensitive your budget is. If you would rather work in the other direction — from income and debts towards a price — the home affordability calculator applies the ratio logic described here for you. Bring both sets of figures to your lender conversation.
Frequently Asked Questions
Is the 28/36 rule based on gross or net income?
Gross — income before tax and deductions. This is one reason the rule feels generous in practice: your take-home pay may be considerably lower, so a payment that passes the 28% test can still consume a large share of the money that actually reaches your account.
Can I get a mortgage if I exceed 36%?
Often, yes. The 28/36 rule is a guideline rather than a legal limit, and many loan programmes allow higher debt-to-income ratios when credit, down payment or reserves are strong. Limits differ by programme and lender and are revised over time, so ask your lender what applies to your situation — and remember that being allowed to borrow more is not the same as it being wise to.
Does the rule change if I have a large down payment?
The ratios themselves do not change, but the outcome does. A bigger deposit means a smaller loan, a smaller payment, and possibly no mortgage insurance — so the same 28% housing budget stretches to a higher purchase price.
Should student loans count if they are in deferment?
Usually something is counted. Different programmes handle deferred or income-driven student loans differently, and some substitute a calculated percentage of the balance when no payment is due. Check with your lender rather than assuming a deferred loan is invisible.
Why is my pre-approval higher than what I calculated?
Pre-approvals are based on the lender's underwriting standards, which may permit a higher back-end ratio than 36%, and they exclude everyday costs like childcare, saving, insurance excesses and travel. The gap is normal. It is a ceiling, not a recommendation.
Sources
- The 28/36 rule — a long-standing mortgage underwriting guideline widely used by lenders and housing counsellors to screen front-end (housing) and back-end (total debt) ratios.
- Consumer Financial Protection Bureau — consumer guidance on mortgages, debt-to-income ratio, loan estimates and closing costs (referenced by name).
- Fannie Mae Selling Guide — eligibility and debt-to-income requirements for conventional loans (referenced by name).
- U.S. Department of Housing and Urban Development / Federal Housing Administration — housing-ratio and mortgage-insurance guidance for FHA loans (referenced by name).