28/36 Rule Calculator

Written by Great Medico

Updated September 25, 2026 •3 min read

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28/36 Rule Calculator is most useful when the result stays tied to the assumptions that produced it. It turns income, debt, rate, term, and ratio assumptions into a planning ceiling for a car price or housing payment.

What this calculator does

28/36 Rule Calculator turns income, debt, rate, term, and ratio assumptions into a planning ceiling for a car price or housing payment. The form asks for gross monthly income, other monthly debt payments, housing ratio limit and total debt ratio limit. The result should therefore be read as a calculation from those displayed assumptions, not as live market, lender, tax, or government-program data unless the page explicitly supplies such a feed.

How to use it

Enter Gross monthly income, Other monthly debt payments, Housing ratio limit and Total debt ratio limit. Keep monetary inputs in one currency; the currency selector formats results and does not convert exchange rates. Enter rates and percentages on the scale shown by the field label; do not silently switch between a decimal and a percent. Keep time values in the period shown on the form so a monthly figure is not accidentally entered as an annual one or vice versa. Before calculating, recheck Gross monthly income, Other monthly debt payments, Housing ratio limit against the source values you intend to model. If a default value is already filled in, confirm that it matches the scenario you actually want to test rather than assuming the preset is current or personally appropriate.

How the calculation works

The car tool limits a target payment to the entered percentage of gross monthly income, converts that payment to a loan amount with the entered rate and term, adds down payment and trade-in value, and adjusts for sales tax. The 28/36 tool compares the front-end housing limit with the back-end total-debt limit after other monthly debt. This is the calculation method to use when checking the result from 28/36 Rule Calculator; values not represented by a visible input should not be inferred as part of the model.

Example

With $8,000 gross monthly income, a 28% housing limit gives $2,240. A 36% total-debt limit gives $2,880; after $800 of other monthly debt, that leaves $2,080 for housing. The calculator uses the lower $2,080 figure.

How to interpret the result

The result is a screening ceiling, not a lender approval. Lower debt, a larger down payment, or a lower rate can increase modeled affordability; stricter ratio targets reduce it. Compare alternative inputs on the same basis rather than treating one output as a universal cutoff.

Limitations and notes

Lenders use credit, verified income, debt definitions, taxes, insurance, reserves, program rules, and underwriting standards that are not fully represented here. In the current car-affordability implementation, the visible “other monthly debt” field does not reduce the target payment, so treat that result cautiously. Any cost, rule, or cash flow without a visible input remains outside the model.