The federal income tax is a pay-as-you-go tax. There are two ways to pay as you go.
Withholding
If you are an employee, your employer probably withholds income tax from your pay. Tax may also be withheld from certain other income — including pensions, bonuses, commissions, and gambling winnings. In each case, the amount withheld is paid to the IRS in your name.
Estimated tax
If you do not pay your tax through withholding, or do not pay enough tax that way, you might have to pay estimated tax. People who are in business for themselves generally will have to pay their tax this way. You may have to pay estimated tax if you receive income such as dividends, interest, capital gains, rent, and royalties. Estimated tax is used to pay not only income tax, but self-employment tax and alternative minimum tax as well.
Salaries and Wages
Income tax is withheld from the pay of most employees. Your pay includes your regular pay, bonuses, commissions, and vacation allowances. It also includes reimbursements and other expense allowances paid under a non-accountable plan. See Supplemental Wages, later, for more information about reimbursements and allowances paid under a non-accountable plan.
Topic Number 307 - Backup Withholding
When it applies, backup withholding requires a payer to withhold tax from payments not otherwise subject to withholding. You may be subject to backup withholding if you fail to provide a correct taxpayer identification number (TIN) when required or if you fail to report interest, dividend, or patronage dividend income.
Banks or other businesses that make certain types of payments to you must file an information return with the IRS on Form 1099 showing payments that you received during the year. A Form 1099 includes your name and TIN such as a social security number (SSN), employer identification number (EIN), or individual taxpayer identification number (ITIN). The Form 1099 will also report any amounts withheld under the backup withholding rules.
Payments subject to backup withholding: Backup withholding can apply to most kinds of payments reported on Form 1099, including:
https://www.irs.gov/taxtopics/tc307
