The formula to find the gross debt service ratio formula is derived from principal amount, property tax, heating costs and gross monthly income. The sum of the principal, property tax and heating costs divided by the GMI expressed in percentage is GDSR.

Where,

GDSR = Gross Debt Service Ratio

p = Principal and Interest

t = Property Taxes

h = Heating Costs

m = Gross Monthly Income

Additional payments involved in gross debt service ratio (GDSR) are secondary financing, condominium fees and rent paid.