Use your gross income. The common budgeting rule that says you shouldn’t spend more than 30% of your income on rent is based on your total, un-taxed income.  We’ve given you two ways to calculate your rent-to-income ratio above.  The first calculator will provide a percentage based on gross monthly income and the rent amount. The second calculator will let you customize the ratio and provide target amounts for both the gross monthly income and the gross annual income.