Withholding is the amount of income tax your employer pays on your behalf from your paycheck. The changes to the tax law could affect your withholding.
Use the IRS Withholding Estimator to estimate your income tax and compare it with your current withholding. You’ll need your most recent pay stubs and income tax return.
The results from the calculator can help you figure out if you need to fill out a new Form W-4 for your employer. Or, the results may point out that you need to make an estimated tax payment to the IRS before the end of the year.
If you adjusted your withholding part way through 2019, the IRS recommends that you check your withholding amounts again in early 2020 to ensure the right amount is being withheld.
If you're changing your tax withholding, you'll need to know your adjusted gross income (AGI). You can find your AGI number on your prior year’s tax return. If you don’t have a copy of last year’s tax return, you can get it from a tax return transcript.