28/36 Rule Calculator (housing & total debt limits, affordable payment & loan)

Understanding the 28/36 rule calculator — concept and principle

This calculator applies the 28/36 rule, a long-standing US mortgage guideline, to your income and debts. It shows the maximum housing payment under both tests, which test limits you, your current front-end and back-end ratios, and the loan amount that payment could support at a given rate and term. Use it when setting a home-buying budget or checking a planned payment before talking to a lender.

The 36% total-debt test is tighter here because $700 of other debts already use part of it.

How it is calculated

Front-end limit = 28% × gross monthly income (housing costs only).
Back-end room for housing = 36% × gross monthly income − other monthly debt payments.
Maximum housing payment = the lower of the two.
Front-end ratio = housing payment ÷ income; back-end ratio = (housing + other debts) ÷ income.
Principal-and-interest budget = maximum housing payment − tax, insurance and HOA.
Loan supported: PV = payment × (1 − (1 + i)^−n) ÷ i, with monthly rate i and n monthly payments.

The principle

Lenders look at two ratios. The front-end (housing) ratio checks whether the home itself is affordable; the back-end (total debt) ratio checks whether housing plus car loans, student loans and card minimums leave enough room for living costs. Using gross income makes the ratios easy to compare between borrowers. The loan amount comes from the present value of an annuity: the sum today that a level monthly payment can repay over the term at the given rate.

Worked example

Default inputs: income $8,000, other debts $700, planned housing $2,100 (including $500 tax, insurance and HOA), 6.5% for 30 years.

Front-end limit = 0.28 × 8,000 = $2,240.
Back-end room = 0.36 × 8,000 − 700 = $2,180, so the 36% test applies: $2,180.
Your ratios: 2,100 ÷ 8,000 = 26.3% front-end; (2,100 + 700) ÷ 8,000 = 35% back-end. Within both limits.
P&I budget = 2,180 − 500 = $1,680; i = 0.065 ÷ 12, n = 360.
Loan supported = 1,680 × (1 − (1 + i)^−360) ÷ i ≈ $265,794.

Each point is the calculator re-run with only “Gross monthly income (before tax)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Gross monthly income (before tax)	Maximum housing payment (both tests)
2,000	$20
4,000	$740
6,000	$1,460
8,000	$2,180
10,000	$2,800
12,000	$3,360
16,000	$4,480

How to read the result

Where does your result fall?

If your ratios are under 28% and 36%, your planned payment fits the guideline. The limit that applies tells you which side to work on: high other debts make the back-end test bind, as here. The loan amount is not a price limit; add your down payment to estimate a home price. Many loan programmes allow higher ratios, and your own budget may call for lower ones.

Common mistakes

Using take-home pay instead of gross income.
Leaving out property tax, insurance or HOA from the housing payment.
Forgetting minimum payments on cards, car loans or student loans.

Keep in mind: The 28/36 rule is a rule of thumb, not a law or a loan approval. Lenders use their own criteria, credit scores and programme rules. This is not financial advice.

Frequently asked questions

Is the 28/36 rule still used?

It remains a common guideline, but many loan programmes accept higher debt-to-income ratios.

Does the 28% include property tax and insurance?

Yes. It covers principal, interest, property tax, insurance and HOA dues.

What counts as other debt?

Recurring monthly obligations such as car loans, student loans, credit card minimums and personal loans.

Sources: Standard annuity present-value formula for a level-payment loan (OpenStax, Principles of Finance (2022), Ch. 8 Time Value of Money II: Equal Multiple Payments)

Checked 9 Nov 2026. The 28% housing / 36% total-debt guideline is a common US mortgage rule of thumb (no single official source); loan amount from a level monthly payment: standard annuity formula.

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