28/36 Rule Calculator estimates the maximum monthly housing payment supported by your gross income and existing debts, using the traditional front-end and back-end DTI ratios.
Estimate Maximum Affordable Housing Payment Using the 28/36 Debt-to-Income Guideline
This calculator estimates the largest monthly housing payment your income and existing debt could support, using the traditional 28/36 debt-to-income guideline. It’s built for homebuyers sizing up affordability before talking to a lender, not for anyone already in the underwriting process.
What to Enter and What the Results Show
Enter gross annual income, your recurring monthly debts (auto, student loan, credit card, other), and estimated monthly property taxes and insurance. Results show your maximum housing payment under both the 28% front-end and 36% back-end ratios, whichever is stricter, plus the principal-and-interest room left after escrow and which limit is actually constraining you.
How the 28% and 36% Limits Are Calculated
This tool applies the 28/36 rule: your total housing payment shouldn’t exceed 28% of gross monthly income (the front-end ratio), and your total debt, housing included, shouldn’t exceed 36% (the back-end ratio). The math takes the stricter of the two:
$$H = \min(0.28I,\ \ 0.36I – D)$$
I is gross monthly income and D is your existing monthly debt payments, before the new mortgage. Whichever number is lower becomes your maximum housing payment. Subtracting estimated property tax and insurance from that leaves the principal-and-interest room for the loan itself.
The 28/36 rule is a long-standing lending convention, not a law or a fixed underwriting requirement. Actual limits vary by loan program: Fannie Mae’s automated underwriting can approve a back-end DTI up to 50%, FHA allows a 31% front-end and 43% back-end ratio (higher with compensating factors), and VA loans skip a front-end cap entirely and use a 41% back-end guideline built around residual income instead.
The CFPB’s Qualified Mortgage rule used to cap DTI at 43% for certain legal protections; since 2021 it uses a price-based test instead, comparing a loan’s APR to the Average Prime Offer Rate. The 28/36 numbers here are a traditional benchmark, not necessarily what a lender will actually approve.
The most common input mistake is entering an annual debt figure into a field that expects a monthly payment, which overstates monthly obligations roughly twelvefold and makes the back-end limit look far stricter than it is.
Gross income has to be greater than zero, or there’s no ratio to calculate. Debt and escrow fields accept zero but not negative numbers. If existing debt alone already exceeds 36% of income, the back-end limit goes negative; the calculator floors it at zero rather than show a negative housing budget, meaning no further home purchase fits this guideline until debt comes down. If escrow exceeds the housing limit, principal-and-interest capacity is floored at zero the same way.
None of this is a loan approval or a promise from any lender. It’s a projection based on the ratios and numbers you enter, not tax, legal, or financial advice, and an actual underwriter will apply their own program’s rules, not just these two ratios.
One Debt Rule Most Calculators Miss: Short-Term Debt
This calculator adds every debt payment you enter, in full, regardless of how long it lasts. Real underwriting doesn’t always work that way. Under Fannie Mae’s Selling Guide (sections B3-6-05 and B3-6-07), an installment loan with 10 or fewer monthly payments left, a car loan almost paid off, for example, can often be excluded from the debt-to-income calculation entirely.
If your auto loan has 8 payments remaining, a real lender might drop it from your back-end ratio and free up that amount for housing. This tool doesn’t know your remaining loan terms, so if any of your debts are nearly paid off, your real back-end limit could be higher than what’s shown here.
Which Limit Binds and Where the Housing Budget Goes
The left side shows why the lower number wins: even though 28% of income allows $2,333, existing debt pulls the back-end allowance down to $2,200, and that becomes the real ceiling. The right side shows where that $2,200 actually goes once escrow is set aside, leaving $1,850 for principal and interest.
Common Questions About This 28/36 Rule Calculator
What do “front-end” and “back-end” ratio mean?
Front-end is your housing payment (PITI) divided by gross income. Back-end is all your debt, housing included, divided by gross income. The 28/36 rule caps them at 28% and 36%.
Is 28/36 the actual limit lenders use today?
Not usually. It’s a traditional guideline. Fannie Mae’s automated underwriting can approve back-end ratios up to 50%, and FHA and VA loans use their own, often higher, thresholds.
Why did my Max Affordable Housing come out below 28% of income?
Your existing debt pulled the back-end ratio below the front-end cap. The calculator uses whichever limit is stricter, so debt can shrink your housing budget below the 28% ceiling.
Does this account for debt I’m almost done paying off?
No. It counts every debt payment in full. Fannie Mae’s guidelines often let lenders drop installment debt with 10 or fewer payments left, which this calculator doesn’t model.
Can Max Affordable Housing show as zero?
Yes, if existing debt already exceeds 36% of income before any new mortgage. The calculator floors the result at zero instead of showing a negative housing budget.