How lenders determine what loan I can afford (Debt-to-Income ratio)

36% or LOWER debt-to-income ratio is a number that lenders use  to see if you have the ability to manage monthly payments to pay for your house loan.  20% or below is considered an excellent DTI.  If it is higher and 36%, it may be hard to get a loan.  Just remember that your Gross Monthly income is the amount of money you have earned BEFORE  your taxes and other deductions are taken out.  And monthly payments are your bills for your car, house, credit card, school loans, etc.  

     How did they come about that number? Evidence from studies showed that borrowers with higher than 36% DTI  ( Debt to Income) Ratio  tend to have more difficulty with being able to pay their debt.  Sometimes there are exceptions.  You can consult with your chosen lender about this.