Debt-to-Income Calculator Formula

Understand the math behind the debt-to-income calculator. Each variable explained with a worked example.

Use the Debt-to-Income Calculator

Formulas Used

Back-End DTI (Total)

back_end_dti = total_debt / gross_monthly_income * 100

Front-End DTI (Housing)

front_end_dti = monthly_housing / gross_monthly_income * 100

Total Monthly Debt Payments

total_monthly_debt = total_debt

Income After Debt

remaining_income = gross_monthly_income - total_debt

Max Housing at 28% Front-End

max_housing_at_28 = gross_monthly_income * 0.28

Max Total Debt at 43% Back-End

max_total_at_43 = gross_monthly_income * 0.43

Variables

VariableDescriptionDefault
gross_monthly_incomeGross Monthly Income(USD)8000
monthly_housingMonthly Housing (PITI)(USD)2200
car_paymentsMonthly Car Payments(USD)450
student_loansMonthly Student Loans(USD)300
credit_card_minimumsMonthly Credit Card Minimums(USD)150
other_debtOther Monthly Debt Payments(USD)0
total_debtDerived value= monthly_housing + car_payments + student_loans + credit_card_minimums + other_debtcalculated
non_housing_debtDerived value= car_payments + student_loans + credit_card_minimums + other_debtcalculated

How It Works

Debt-to-Income Ratios

Lenders use DTI ratios to assess your ability to manage monthly payments and repay debts.

Front-End Ratio (Housing)

Front-End DTI = Monthly Housing Cost (PITI) / Gross Monthly Income x 100

Most lenders prefer this to be 28% or less.

Back-End Ratio (Total)

Back-End DTI = Total Monthly Debt / Gross Monthly Income x 100

Most conventional lenders want this at 43% or less. FHA allows up to 50% with compensating factors.

DTI Guidelines by Loan Type

  • Conventional: 28% front / 43% back (max 50% with strong file)
  • FHA: 31% front / 43% back (up to 50% with compensating factors)
  • VA: No front-end limit / 41% back (flexible with residual income)
  • USDA: 29% front / 41% back

    • Worked Example

    Gross monthly income of $8,000. Housing $2,200, car $450, student loans $300, credit cards $150.

    gross_monthly_income = 8000monthly_housing = 2200car_payments = 450student_loans = 300credit_card_minimums = 150other_debt = 0
    1. 01Front-end DTI: $2,200 / $8,000 = 27.5%
    2. 02Total debt: $2,200 + $450 + $300 + $150 = $3,100
    3. 03Back-end DTI: $3,100 / $8,000 = 38.75%
    4. 04Both ratios are under typical limits (28% front, 43% back)
    5. 05Remaining income after debt: $8,000 - $3,100 = $4,900
    6. 06Maximum housing at 28%: $8,000 x 0.28 = $2,240
    7. 07Maximum total debt at 43%: $8,000 x 0.43 = $3,440

    Ready to run the numbers?

    Open Debt-to-Income Calculator