The form guides you through the process and it depends on if you are an employee or self employed. You have to complete form 433A/B in order to complete this as well. Current costs of doing business and taxes are part of the calculation so that it comes out to "net" income. Although this form may seem simple, it is not always so simple and you may benefit form the services of an attorney or tax professional (CPA) to complete it right the first time.
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature.
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Generally, you'll enter gross wages (if an employee) then enter the allowable deductions below. If you're self employed, you'll enter the net income of the business activity as "income" and go from there.
Evan A. Nielsen is licensed to practice law in California and handles federal tax matters throughout the U.S. The information provided here is for educational purposes only and is not intended as legal advice for a particular matter. This response does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult an attorney.