The standard lender benchmark says your housing payment should not exceed 28% of your gross monthly income, while total monthly debt, including the future mortgage, should stay under 36%. That second cap is what makes existing debts so important: a $500 car payment does not just shrink the room in your budget for housing, it actively lowers the home price you can qualify for. Working backward from those two ratios, your down payment, and the loan's interest rate gives you a realistic ceiling instead of the optimistic listing-price range that often floats around real estate sites. The Home Affordability Calculator runs exactly that reverse calculation: it applies the 28/36 rule to find your maximum monthly housing payment, runs that payment through the inverse of a mortgage amortization formula to recover the largest loan it can support, and adds your cash down payment to land on a home price you can actually carry.
Why the 28/36 Rule Sets Your Real Ceiling
Most first-time buyers have heard some version of the "two to three times your salary" rule of thumb. It is a useful starting line, but lenders do not actually underwrite that way. They underwrite to a debt-to-income (DTI) ratio, and the most widely cited version is the 28/36 rule documented by the Consumer Financial Protection Bureau and explained in detail on the Wikipedia debt-to-income ratio page.
The rule has two parts. The front-end ratio limits housing costs to 28% of gross monthly income. The back-end ratio limits all recurring debt — the future mortgage plus car loans, student loans, and minimum credit-card payments — to 36% of gross income. Your maximum housing budget is the smaller of those two numbers, expressed as the formula max payment = min(0.28 × income, 0.36 × income − monthly debts), clamped to zero if your debts already exceed 36%.
When other debts are low, the front-end 28% ratio usually binds. When existing debts are heavier, the back-end 36% ratio pulls the number down. With very high existing debt, the budget can drop to zero, which is the calculator's way of telling you it is time to pay something off before house-hunting. Knowing which ratio is binding for your situation explains why two buyers with identical incomes can qualify for very different home prices.
What the Home Affordability Calculator Does Differently
A standard mortgage calculator starts with a loan amount and computes the monthly payment. That is the right tool when you have already picked a home and want to know what the payment looks like. It is the wrong tool for the first question every buyer actually asks, which is: starting from my income and debts, what is the biggest home I can realistically target?
The Home Affordability Calculator reverses the workflow. It takes your gross monthly income and your existing monthly debt payments, applies the 28/36 rule to derive a maximum housing payment, then uses the annuity present-value formula in reverse to figure out the largest loan that payment can support over your chosen term and interest rate. Finally it adds your cash down payment to surface a single number — the maximum home price in your realistic range. Every calculation runs entirely in your browser, so nothing you type is uploaded, saved, or shared.
Calculate Your Affordable Home Price
- Enter your gross monthly income, or your annual income and toggle to the annual setting, so the calculator can work in a consistent monthly frame. Use gross, not net, because lenders underwrite against gross income.
- Add up every recurring monthly debt you currently owe — car loans, student loans, credit-card minimums, personal loans, child support or alimony — and enter the total. Skip utility bills and subscriptions; only obligations that appear on a credit report count toward DTI.
- Enter the cash down payment you can actually bring to closing, your expected annual interest rate, and the loan term in years (commonly 30 or 15).
- Read the three outputs: the affordable home price, the affordable loan amount (which equals home price minus down payment), and the maximum monthly housing payment that drove both numbers.
- Change any single input to see the trade-off instantly. Pay off a car, raise the down payment, or shorten the term and watch the home price move with each adjustment.
A Worked Example With the Two Ratios
To make the math concrete, take a buyer with $7,000 in gross monthly income and $500 in current monthly debt payments (a car loan plus a small student loan balance). The two ceilings are:
- Front-end: 0.28 × $7,000 = $1,960
- Back-end: 0.36 × $7,000 − $500 = $2,520 − $500 = $2,020
The binding constraint is the smaller number, $1,960, because the front-end ratio is the tighter cap once debts are modest. That $1,960 is the most this buyer can comfortably put toward principal and interest each month. The next step is to translate $1,960 per month into a maximum loan over, say, 30 years at 7% interest, using the inverse of the standard mortgage amortization formula. Because the answer depends on the interest rate and term, the easiest way to see the final loan amount and the resulting home price (loan plus your down payment) is to enter the same numbers into the Home Affordability Calculator and let it run the annuity present-value math for you.
How Your Inputs Change the Result
Each input has a different kind of leverage on the final home price. The table below describes the direction and rough scale of each effect without quoting specific dollar figures, because the actual numbers depend on the rate and term you choose. Run any combination through the calculator for the exact figure.
| Change you make | Effect on max home price | Why it moves |
|---|---|---|
| Pay off a $300/month car loan | Rises meaningfully | Back-end ratio frees up $300 of debt room, raising the binding payment ceiling |
| Add $20,000 to your down payment | Rises by roughly $20,000 | Loan needed shrinks one-for-one with the down payment |
| Switch from 15-year to 30-year term | Rises substantially | Lower monthly payment supports a much larger loan at the same rate |
| Drop interest rate from 7% to 6% | Rises modestly to noticeably | Inverse amortization stretches the same payment over cheaper money |
| Add a co-borrower's income | Rises significantly | Both 28% and 36% ceilings scale with combined gross income |
| Existing debts already exceed 36% of income | Drops to zero | Back-end ratio is exhausted, leaving no room for a housing payment |
What the Estimate Leaves Out
The 28/36 estimate is a lender-style ceiling, not your total monthly cost of owning the home. The calculator covers loan principal and interest only. Your true monthly outlay will also include property taxes, homeowners insurance, HOA or condo fees, and, if your down payment is under 20%, private mortgage insurance (PMI). Each of those line items reduces how much house you can comfortably carry on the same income, because they all come out of the same monthly cash flow the 28% front-end ratio was designed to protect.
The 28/36 rule is also a guideline rather than a guarantee. Real underwriting weighs your credit score, cash reserves after closing, employment history, and the specific loan program. FHA, VA, and conventional loans each apply their own DTI limits, and some lenders will stretch ratios higher for strong borrowers. Treat the calculator's output as a realistic benchmark for your search and your budget conversation, then confirm the actual approved amount with a licensed mortgage professional before you make an offer.
Using the Number Without Misleading Yourself
A reasonable buyer treats the affordable home price as the top of the search range, not the target. Bidding at the ceiling leaves no margin for repairs, moving costs, the first few years of higher utility bills, or a job interruption. A common habit is to subtract 10 to 15% from the calculator's output and treat that as the price you actively shop for, which keeps the same monthly cash flow available for the costs the 28/36 rule does not capture.
The same calculator also doubles as a planning tool. Before you start touring homes, run it with your current debts, then run it again with the debts you would have after paying off a car or a credit-card balance. The difference in affordable price tells you, in dollars, exactly how much that payoff is worth in housing budget. Run it with a 15-year term and a 30-year term and see the trade-off between monthly breathing room and total interest. Each adjustment recalculates instantly, which is what makes the reverse approach so much more useful than guessing from a listing price and hoping the payment will fit.
If you're weighing options, Is a Home Affordability Calculator Safe to Use Online? covers this in detail.
If you're weighing options, Home Affordability Calculator by Income: What It Covers covers this in detail.