Mortgage Allowance Calculator

“Allowance” on this page means one thing only: the maximum monthly housing payment a lender guideline allows on your income. It is not an employer subsidy and it is not a benefit payment. Enter your gross monthly income and your non-housing debts and the calculator applies the conventional 28/36 rule, shows both allowances side by side, names the rule that binds, and tests a proposed payment against both ratios.

Quick Answer

How to use the mortgage allowance calculator

Three entries produce the answer: gross monthly income, non-housing debts, and an optional proposed payment to test. The calculator then returns both allowances, the maximum payment and the binding rule.

1. Enter gross monthly income. Use pay before tax. A salary of $120,000 a year is $10,000 a month; hourly workers can multiply their hourly wage by hours per week, then by 52, then divide by 12.
2. Add your non-housing debts. Total the minimum payments on car loans, cards, student loans and other recurring debts from your credit report. Leave the field blank and the tool counts $0, which flatters the back-end allowance, so blank should mean genuinely debt-free.
3. Optionally test a proposed payment. Enter a full PITI payment from a listing or a lender quote. You get its two ratios plus a plain verdict: within guidelines with headroom, or over by a stated amount.
4. Read which rule binds. That single line tells you whether your ceiling is set by housing costs or by your other debts, and therefore whether paying a debt down actually buys you more house.

Once you have a payment ceiling, the next step is turning it into prices: run candidate payments through a mortgage payment calculator at current rates and compare the full PITI figure, not the loan amount, against your allowance.

The 28/36 formula, line by line

The math is two multiplications and a subtraction. Front-end allowance = gross monthly income \u00d7 28%. Back-end allowance = gross monthly income \u00d7 36% \u2212 non-housing debts. Maximum housing payment = the lower of the two.

The 28% ceiling covers housing alone, which is why underwriters call it the housing or front-end ratio. The 36% ceiling covers every recurring debt including the new housing payment, which is why it is called the total debt or back-end ratio. Lenders formalise both ideas in their debt-to-income guidance: Fannie Mae’s Selling Guide section on debt-to-income ratios sets the manual underwriting benchmarks, and the Consumer Financial Protection Bureau’s explanation of the debt-to-income ratio covers why the separate 43% qualified-mortgage threshold also exists in federal rules. If you want your ratios stated as percentages rather than dollar allowances, a debt-to-income ratio calculator runs the same debts the other way round.

Two quirks of the exact formula are worth knowing before you rely on it. First, the back-end allowance is not floored at zero: debts above 36% of income produce a negative allowance, and this tool prints it as a negative dollar amount rather than hiding it. Second, the tie check treats allowances within one cent as equal, which is why the worked example below reports that both rules bind equally instead of picking a winner on a rounding difference.

Worked example: $10,000 income, $800 debts, $2,600 proposed payment

Every figure in this example reproduces exactly in the calculator above with the pre-filled values. Front-end allowance: $10,000 \u00d7 28% = $2,800. Back-end allowance: $10,000 \u00d7 36% \u2212 $800 = $2,800. The two rules tie, so the maximum housing payment is $2,800.

The proposed $2,600 payment divides to 26.0% of income on its own and 34.0% once the $800 of other debts is added, so the tool’s verdict is “within guidelines” with $200 a month to spare. Push the proposed payment to exactly $2,800 and the headroom falls to $0.00 while the verdict stays within guidelines; one cent more, at $2,800.01, flips it to “exceeds guidelines by $0.01”. The boundary is the allowance itself, with no hidden cushion.

Allowances at common incomes and debt levels

The maximum payment is the lower allowance in each row, and the pattern teaches the rule faster than any definition: at low debts the 28% housing cap binds, and once debts pass 8% of income the back-end cap takes over. Every cell below is the calculator’s own output for those inputs.

Gross monthly income	Front-end (28%)	Back-end, $0 debts	Back-end, $500 debts	Back-end, $1,000 debts	Maximum payment at $1,000 debts
$5,000	$1,400	$1,800	$1,300	$800	$800
$7,500	$2,100	$2,700	$2,200	$1,700	$1,700
$10,000	$2,800	$3,600	$3,100	$2,600	$2,600
$15,000	$4,200	$5,400	$4,900	$4,400	$4,200

Read the $15,000 row carefully: even with $1,000 of debts the front-end cap of $4,200 still binds, because the back-end allowance of $4,400 sits above it. Debt only becomes the binding problem once it is large relative to income, which is exactly the situation the back-end rule exists to catch.

Which rule binds, and what to do about it

The binding rule is whichever allowance is lower, and it decides your best move. A front-end bind means your income alone sets the ceiling; a back-end bind means your debts do, and debts can be changed before you apply.

When the back-end rule binds, clearing a payment is unusually powerful: retire a $400-a-month car loan and the back-end allowance rises by exactly $400, because the formula subtracts debts dollar for dollar. No other common pre-application move buys payment room that directly. Lenders know this, which is why loan officers so often tell buyers to clear a vehicle loan or a card balance before filing the application rather than after.

When the front-end rule binds, debt paydown buys nothing on this test. Your levers are a higher documented income, a cheaper home, or a loan program with a higher front-end guideline. That is also the point where a seller-funded rate buydown can help the monthly payment fit, although it does not change the ratios a lender qualifies you on: the mortgage buydown calculator prices those structures separately.

The FHA and VA difference

Government-backed programs run looser ratios than conventional 28/36, so this calculator’s answer is the conservative one. FHA guidance in the FHA Single Family Housing Policy Handbook 4000.1 works around a 31% front-end and 43% back-end starting point, with approvals above that where compensating factors are documented.

On the worked example, $10,000 of income with $800 of debts, an FHA back-end calculation gives $10,000 \u00d7 43% \u2212 $800 = $3,500, a full $700 above the conventional $2,800. VA loans take a different route again: the VA uses a 41% total-debt guideline alongside a residual-income test rather than the 28/36 pair, as set out in the VA home loan application guidance. None of that makes the conventional answer wrong; it makes it a floor. If you pass 28/36, you pass the strictest common screen, and anything a program allows above it is headroom you chose not to spend.

What competing calculators miss

Most affordability calculators answer a different question and hide this one. The gaps below came from checking the top-ranking tools for this keyword against the code on this page.

• They convert straight to a home price. The big affordability tools bury the payment ceiling inside a price estimate built on their own rate, tax and down-payment assumptions. Change the assumed rate and the “affordable” price swings by tens of thousands, while the 28/36 payment ceiling, the number underwriting actually applies first, never appears.
• They show one number with no binding rule. A single maximum tells you nothing about whether housing or debts produced it, so you cannot tell whether clearing a loan would help. This page names the binding rule on every run.
• They never test your actual payment. A proposed-payment check with both ratios and a headroom figure is the step a buyer actually needs before an offer. Rivals leave you to do that division yourself.
• They hide the negative case. When debts exceed the back-end cap, most tools quietly clamp the answer at zero. This one prints the negative allowance, because “you are $400 past the total-debt ceiling before any housing payment” is more useful than a silent zero.

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