This Illinois alimony calculator makes Illinois maintenance calculations using the Illinois alimony formula. To calculate Illinois guideline maintenance, you must enter gross income, child dependent, and marriage length information into the calculator.This calculator is intended to be used only as a general tool to estimate potential splits and payments. Illinois has established a specific formula for calculating the amount and duration of spousal maintenance obligations or awards. Get an estimate for alimony payments and duration. Get an idea on how much money a month you can expect to pay, and for how you can expect to pay it. Calculate alimony quickly and accurately with our state-specific alimony calculators. Get an estimate based on your state's guidelines for free. Learn about the types of alimony available in Illinois, how it's calculated, and the factors courts consider when awarding spousal maintenance. Step 2: Input Data into the Calculator.