There are several websites that have a child support calculator on them to help you estimate what you (or the other parent) will pay in child support.
Look on the Texas Attorney website for information regarding Texas child support.
The Texas Attorney General has a child support calculator on their site.
You will find that each calculator might be a little different.
I don't know why.
There is a paid I-phone application called Texas CS Calculator available for under $10.
Child support is based on a chart in Texas.
You start with a person's gross weekly, monthly or annual income.
I can promise you that the net income for Texas will NOT match a person's paystub for a variety of reasons - miscellaneous deductions, federal income tax withholding is different than what the State of Texas thinks it should be, etc.
All sources of income are used to determine child support - not just a person's income.
For example, there was a father than did not work. He worked several office buildings in downtown Houston. His federal income tax form showed his income to be over $500,000/year. He did not think he should pay child support because he did not work but merely managed his properties. The judge ordered his child support based on the income from other sources on his tax return.
Items like bonuses, rental income, investment income, second jobs, over-time, etc. is used to calculate child support.
If you are "purposely under-employed" then child support will be based on the job that you should have.
For example, an engineer making $200,000 a year quit to become a grocery store bagger. The judge set this person's child support based on an annual income of $200,000 year. This parent was free to work as a bagger but since this parent had been an engineer and had voluntarily quit being an engineering job the judge determined he was "purposely under-employed" to avoid paying child support.
The Texas Family Code is available for free. You can read it.
It contains the definition of "net income" and the chart for determining child support.
If you don't work, then your child support will be set at minimum wage at 40 hours per week. That comes out to approximately $225/month. You don't have to work but you are obligated to support your minor child in the State of Texas. Even prisoners are ordered to pay child support in Texas within 30 days of getting out of prison.