Arizona Chapter 13 Calculation of Your Disposable Income is a bankruptcy calculation that determines the amount of money a debtor has available to repay creditors. This calculation is based on the debtor's current monthly income and allowed expenses. There are two types of Arizona Chapter 13 Calculation of Your Disposable Income: Formal and Modified Means Test. The Formal Means Test is based on the debtor's current monthly income, expenses as determined by the Internal Revenue Service, and other factors such as family size. The Modified Means Test is based on the debtor's current monthly income and expenses, but does not take into account family size. Both calculations are used to determine the debtor's disposable income, which is the amount of money available to repay creditors.