The law is unclear on this issue, and we leave it up to you.
The checkbox is on the Deductions > Taxes screen, as shown below:
If you click the checkbox, look at the tax number, and and then clear the checkbox, you will see that the tax number changes.
With the box checked, the payer’s tax typically goes down, as maintenance is deducted from taxable income. With the box cleared, the payer’s tax typically goes up, as no maintenance is deducted.
With the box checked, if you click the link to see the View/Edit Taxes report, the payer’s tax shown on this screen will match the tax shown on the View/Edit Taxes screen, where actual maintenance is deducted.
With the box cleared, the payer’s tax shown on Federal 1040 taxes will not match the tax shown on this screen, because View/Edit Taxes always includes maintenance..
If the box is X’d, the maintenance used in that tax calculation would be the maintenance specified on the Disclosure Statement > Support / Maintce screen, shown below.
Also, the software is doing an “actual” current year tax calculation. So if maintenance is being paid only for two months in the year, the tax calculated for child support purposes will reflect only two months of maintenance.