Here ya go.
How does the court decide how much child support I should pay?
Texas has established a formula to calculate what amount a non-custodial parent should pay for child support. If your net monthly income is less than $6000, Texas law has established the following guidelines for child support payments. The amount withheld is based on your net income each month.
20 percent for one child
25 percent for two children
30 percent for three children
35 percent for four children
40 percent for five children
Not less than 40 percent for six children
Special rules apply in cases of split or joint placement or multiple children in different households.
If a court believes that you are not making as much money as you should, the child support amount may be based on your earning potential. This is income that you could potentially earn.
I believe that in order to increase a child support payment you have to have an increase in salary of about 20%. I also think she can only ask for an increase once evry two years or so.