Are you having enough taxes withheld from your paycheck?

Despite all the attention to tax cuts for most American tax payers, simulations by the Government Accountability Office "suggest 30 million Americans -- 21% of taxpayers -- aren't having enough withheld from their paychecks under the new tax law, meaning they will owe money to the IRS next year. That compares with 18% under the old tax law." (Retirement Security Smartbrief, 8/2/18). Source: https://www.npr.org/2018/08/01/634474267/more-taxpayers-will-owe-the-irs-in-april-due-to-under-withholding-report-says
To estimate your tax liability for the year, use the IRS Withholding Calculator: https://www.irs.gov/individuals/irs-withholding-calculator
To avoid penalties for under payment, file a new form W-4 with your employer(s).  
The Basics of Estimated Taxes for Individuals: https://www.irs.gov/newsroom/the-basics-of-estimated-taxes-for-individuals "The IRS has seen an increasing number of taxpayers subject to estimated tax penalties, which apply when someone underpays their taxes. The number of people who paid this penalty jumped from 7.2 million in 2010 to 10 million in 2015, an increase of nearly 40 percent. The penalty amount varies, but can be several hundred dollars."
"The IRS urges taxpayers to check into their options to avoid these penalties. Adjusting withholding on their paychecks or the amount of their estimated tax payments can help prevent penalties. This is especially important for people in the sharing economy, those with more than one job and those with major changes in their life, like a recent marriage or a new child."

"In general, taxpayers don’t have to pay a penalty if they meet any of these conditions:

• They owe less than $1,000 in tax with their tax return.
• Throughout the year, they paid the smaller of these two amounts:
  • at least 90 percent of the tax for the current year
  • 100 percent of the tax shown on their return for the prior year – this can increase to 110 percent based on adjusted gross income"