You can calculate the federal tax withholding from your gross income, so that you'll know how much your federal tax liability will be each payday. Figuring out your federal tax liability helps you decide if you should have a little extra taken out of your checks each week, so that you won't owe any money when you file your federal taxes. It can also help you determine if you should claim an allowance on your W-4 form, which you file with your employer each year.

No Pre-Tax Deductions

Step 1

Determine your gross pay based on your pay frequency: weekly, bi-weekly, semi-monthly or monthly. For example, if you're paid every two weeks, work 40 hours a week and your hourly wage is $10, your gross pay is $800 for the two-week period.

Step 2

Use IRS Publication 15, which is what employers use to find your tax liability. Start on page 38, and look for your filing status, which is single or married, and your pay period, which is weekly, bi-weekly, semi-monthly or monthly.

Step 3

Look at the tax table to find your gross income from the left side. Look at the top of the chart to find the number of allowances that you claim on your W-4 form. For example, if you're single, claim two allowances and your gross pay is $800 bi-weekly, your federal tax liability is $49.

With Pre-Tax Deductions

Step 1

Determine your gross pay based on your pay frequency: weekly, bi-weekly, semi-monthly or monthly. For example, if you're paid every two weeks, work 40 hours a week and your hourly wage is $10, your gross pay is $800 for the two-week period.

Step 2

Deduct your qualifying pre-tax deductions from your gross pay. For example, if you contribute $50 every pay period to your 401k, subtract that amount from the $800. This leaves you with $750 of taxable gross income. Note: Pre-tax deductions are only subtracted from the gross pay to determine federal and state taxes, not to determine Social Security and Medicare tax.

Step 3

Use IRS Publication 15, which is what employers use to find your tax liability. Start on page 38, and look for your filing status, which is single or married, and your pay period, which is weekly, bi-weekly, semi-monthly or monthly.

Step 4

Look at the tax table to find your gross income from the left side. Look at the top of the chart to find the number of allowances that you claim on your W-4 form. For example, if you're single, claim two allowances and your gross pay after pre-tax deductions is $750 bi-weekly, your federal tax liability is $40.