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Debt-to-Income Ratio Calculator

Computes the back-end debt-to-income ratio (all monthly debt payments including housing divided by gross monthly income) and the front-end ratio (housing payment alone), and compares them with the 28/36 guideline and the 43 % qualified-mortgage benchmark.

When to use

You want to check whether a proposed mortgage or other loan fits typical lender DTI limits, or how much monthly debt capacity remains.

Do not use when: You need to know how long it takes to pay a balance off (use debt-payoff), or the amount of a down payment (use down-payment).

Formula

back_end_dti = (Σ monthly_debts + other_monthly_debt + housing_payment) / gross_monthly_income × 100; front_end_dti = housing_payment / gross_monthly_income × 100

Bands follow common US underwriting practice: the 28/36 rule (housing ≤ 28 %, all debt ≤ 36 %) and the 43 % back-end cap of the original 2014 Qualified Mortgage rule; since 2021 the General QM definition uses a price-based test, but 43 % remains a widely used benchmark and Fannie Mae allows up to 50 % with compensating factors. Utilities, groceries and insurance are not debts.

Inputs

Parameter	Type	Required	Description
`gross_monthly_income`	number	yes	Total pre-tax income per month (salary, bonuses, other verifiable income). Range: > 0, ≤ 100000000
`monthly_debts`	number_list	no	Minimum monthly payments on non-housing debts: car loans, student loans, credit-card minimums, alimony. Omit if you use other_monthly_debt.
`other_monthly_debt`	number	default 0	Additional non-housing debt payments not itemised in monthly_debts (or the whole total if you have it). Range: ≥ 0, ≤ 100000000
`housing_payment`	number	no	Proposed or current monthly housing cost: rent, or mortgage principal, interest, taxes, insurance and HOA (PITI). Enables the front-end ratio. Range: ≥ 0, ≤ 100000000

Outputs

Output	Type	Unit	Description
`total_monthly_debt_payments`	number		Sum of monthly_debts + other_monthly_debt + housing_payment.
`back_end_dti_percent`	number	%	total_monthly_debt_payments / gross_monthly_income × 100.
`front_end_dti_percent`	number	%	housing_payment / gross_monthly_income × 100 (only when housing_payment is given).
`assessment`	string		Band of the back-end ratio: Good (≤ 36 %), Acceptable (36–43 %), High (43–50 %) or Very high (> 50 %).
`max_housing_payment_at_28_percent`	number		0.28 × gross_monthly_income (front-end guideline).
`max_total_debt_at_36_percent`	number		0.36 × gross_monthly_income (conservative back-end guideline).
`max_total_debt_at_43_percent`	number		0.43 × gross_monthly_income (qualified-mortgage benchmark).
`remaining_capacity_at_43_percent`	number		max_total_debt_at_43_percent − total_monthly_debt_payments (negative when already above 43 %).

Example

6,000 income, debts 400/250/150, housing 1,500: {"gross_monthly_income":6000,"monthly_debts":[400,250,150],"housing_payment":1500} → {"total_monthly_debt_payments":2300,"back_end_dti_percent":38.33,"front_end_dti_percent":25,"assessment":"Acceptable (36–43 %)","max_housing_payment_at_28_percent":1680,"max_total_debt_at_36_percent":2160,"max_total_debt_at_43_percent":2580,"remaining_capacity_at_43_percent":280}

8,000 income, 1,600 total debt, no housing given: {"gross_monthly_income":8000,"other_monthly_debt":1600} → {"total_monthly_debt_payments":1600,"back_end_dti_percent":20,"assessment":"Good (≤ 36 %)","max_total_debt_at_43_percent":3440}

GET https://tttkmbb.com/api/v1/calculate/debt-to-income?gross_monthly_income=6000&monthly_debts=400%2C250%2C150&housing_payment=1500

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/debt-to-income (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/debt-to-income · Markdown: https://tttkmbb.com/finance/debt-to-income.md · JSON definition: https://tttkmbb.com/finance/debt-to-income.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="debt-to-income"
OpenAPI operationId: calculate_debt_to_income_ratio
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

CFPB – What is a debt-to-income ratio? (government)
CFPB – Ability-to-Repay and Qualified Mortgage Standards (Regulation Z) (government)
Investopedia – Debt-to-Income (DTI) Ratio: What's Good and How to Calculate It (reference)

FAQ

Gross or net income?

Lenders use gross (pre-tax) income, so enter pay before taxes and deductions; using take-home pay overstates the ratio.

Which payments count as debt?

Recurring obligations that appear on a credit report or court order: loans, credit-card minimum payments, leases, child support. Utilities, phone plans, insurance and groceries are excluded.

Related calculators

Mortgage Payment Calculator — Compute the PITI housing payment to enter here.
Down Payment Calculator — Loan amount and PMI for the purchase.
Debt Payoff Calculator — Clear a balance to lower the ratio.