How to calculate net income to figure out child support payments?

In Texas, there is a chart/formula created by the Texas Attorney General’s Office (AG) that allows spouses to figure out their "net income." The Texas Attorney General's Office calls the net income chart a "tax chart." 
First, to properly calculate child support you need to come to a yearly gross figure. You can find a gross income from your W-2 form, a year-end paystub, or a calculation based upon your year to date on your paystub. 
Second, that figure will be divided by twelve ("12"), giving you a gross monthly income. 
Third, that figure will then be plugged into the tax table found at: http://www.oag.state.tx.us/cs/attorneys/attorneys_other_tax.shtml. 
Instructions are provided in the link to each years tax chart.