This Illinois alimony calculator makes Illinois maintenance calculations using the Illinois alimony formula. Illinois has established a specific formula for calculating the amount and duration of spousal maintenance obligations or awards.Calculate alimony quickly and accurately with our state-specific alimony calculators. Get an estimate based on your state's guidelines for free. Here's an alimony calculator that will help you get an idea of the payments and duration. The Illinois Alimony Calculator is designed to offer estimations based on various input factors, such as income, length of marriage, and specific circumstances. It's definitely better to have the judge say, "Gross income" or "Post-tax income," so you're sure. Calculate the alimony formula and the child support formulas so you can even verify how much each of you should be paying the other. There is no charge for followup questions. § 61.08(6) (2023).) Modifying Rehabilitative or Durational Alimony.