How do I estimate tax liability for my personal tax extension - form 4868

You only need to estimate your tax liability if you plan to make a payment to the IRS with your tax extension. You will use your W-2 form answer the questions.  

1.  Filing Status - single, married filing jointly, married filing separately, head of household and qualifying widower with dependent child.
2. Your Total 2020 Wages - found in BOX 1 of your W-2(s) (wages, tips and other compensation), as well as any other income you have such as dividends, interest and unemployment compensation. 
3. Number Of Additional Dependents - Not including you or your spouse.
4. Your Estimated Tax Liability Calculation Is Based On:
1. You are not itemizing.
2.  You use the standard deduction when you file your return. 

• Does not include payments made to the IRS. Enter all payments made to the IRS to determine if you should expect a refund/owe a payment to the IRS.
• Payments Made To The IRS - This includes Federal income tax withheld - found in Box 2 on your  W-2(s), estimated tax payments, and certain tax credits (Earned Income Credit and Additional Child Credit).