How Do I Calculate My Mortgage Payments Commission Fees For Real Estate Agents How Can I Calculate My Debt To Income Ratio How to Calculate a Debt-to-Income Ratio | Sapling.com – Step. Divide your total monthly debt obligations by your total monthly income. This is your total debt-to-income ratio. Step. Take action if your ratio is higher than 0.36, which industry professionals would call a score of 36.