You should keep in mind that this free online calculator only considers employment income and can only do simple calculations. Use this free calculator to calculate spousal support according to the Canadian Spousal Support Advisory Guidelines, as well as child support (if applicable).Use our calculator for Canadian spousal support estimates to help you understand what your support payments may look like. Find out how your case is registered with the Family Responsibility Office (FRO) to help you pay and receive support. Spousal support calculator in Ontario. The formula is that you take the difference in your annual incomes and multiply that difference time the number of years of cohabitation times. If it's clear that a spouse is deliberately unemployed or underemployed, courts have the authority to impute income. Does retroactive spousal support apply in your case? Call an Ontario divorce lawyer at Feldstein Family Law Group P.C. for additional information and help. Our tool will calculate how much spousal support a judge may order.