Estimate Alimony Payments. Illinois uses a formula outlined in the Illinois Marriage and Dissolution of Marriage Act to calculate spousal maintenance.Find out how alimony is calculated in Pennsylvania and what factors the court considers when deciding spousal support awards. To calculate Illinois guideline maintenance, you must enter gross income, child dependent, and marriage length information into the calculator. Unlike child support and Alimony Pendente Lite (APL), there is no online calculator to determine an exact amount of alimony. In Illinois there are five main types of alimony or spousal support; temporary, fixedterm, reviewable, permanent, and lumpsum. What is the Pennsylvania alimony calculation? Gross Salary: Salary before taxes are taken out. Post-divorce alimony, if awarded, commences once a divorce is complete. Marital Laws Logo Alimony Calculator. MaritalLaws.