Debt-to-Income Ratio Calculator mechanism

Model scope

The core ratio is standard when all inputs are monthly and gross income is pre-tax. The exact ambiguity requiring review is the undefined composition of total monthly debt payments and the unspecified behavior for zero income. Retain the educational-only label and explicitly state that lender definitions, thresholds, and underwriting decisions vary.

• The ratio formula is correct for monthly debt payments divided by gross monthly income, but the stated formula omits the multiplication by 100 required when the output is labeled as a percentage: DTI%=total_monthly_debt_payments/gross_monthly_income×100.
• The specification does not define which obligations must be included in total monthly debt payments, such as housing, installment loans, credit-card minimums, leases, alimony, or other recurring obligations.
• The 36%/43% lender-threshold note is not a computed formula and must be presented as illustrative only, because applicable underwriting thresholds and definitions vary by lender and loan program.

Units and conventions

• Every debt-payment list element is a positive monetary amount in the same currency and monthly period.
• Gross monthly income is pre-tax income, expressed in the same currency and monthly period as the debt payments.
• If income is supplied from an annual figure, it must first be divided by 12; annual income must not be divided directly into monthly debt payments.
• DTI percentage is calculated as (sum of monthly debt payments ÷ gross monthly income) × 100.
• The illustrative 36% and 43% figures are percentages, not decimal ratios, and are not universal lending rules.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "monthly_debt_payments": [
      1500,
      300,
      200
    ],
    "gross_monthly_income": 5000
  },
  "expected_outputs": {
    "total_monthly_debt_payments": 2000,
    "dti_percent": 40,
    "threshold_note": "Illustrative reference only: 36% and 43%; actual lender criteria vary."
  },
  "working": "1. Sum debt payments: 1,500 + 300 + 200 = 2,000. 2. Divide by gross monthly income: 2,000 ÷ 5,000 = 0.40. 3. Convert to a percentage: 0.40 × 100 = 40%. 4. Result: DTI = 40%."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

A zero gross monthly income produces an undefined division; an implementation that does not reject it may expose Infinity or an invalid DTI percentage.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json