The U.S. tax system is a pay-as-you-go process. Taxes must be paid as income is earned or received during the year. With the new tax laws, the way tax is calculated for most taxpayers has changed. In addition, any change in your tax situation for the year (e.g., selling stock, changing marital status, working multiple jobs, etc.) can affect how much tax needs to be paid during the year.
If you receive salaries, wages, pensions, unemployment compensation and any taxable Social Security, you can adjust the amount of tax withheld. Some income is not subject to withholding, including income from self-employment or rental activities. Therefore, some of you may need to make estimated tax payments unless you expect to owe less than $1,000 when you file or if you had no tax liability in the prior year (subject to certain conditions).

Making an adjustment to withholding or making an estimated tax payment now may help you avoid an unexpected year-end tax bill and a potential penalty.