The debt-to-income limit for a Federal Housing Administration loan is 31 percent for the mortgage and 43 percent for the mortgage plus all other installment and revolving debt. These limits are designed to prevent buyers from choosing a house they can't afford, according to FHA.com.
To calculate the complete mortgage payment, the FHA adds principal, interest, mortgage insurance, and escrow amounts for insurance and taxes. The organization then divides that number by the applicant's gross monthly income to find the ratio, which can't exceed 31 percent as of 2015, notes FHA.com. The FHA then adds the mortgage payment to all other recurring debt, such as car payments and student loans. The FHA divides the total of the fixed payments by the applicant's gross monthly income, and that number can't exceed 43 percent.