The federal income tax is a pay-as-you-go tax. You must pay taxes as you earn or receive income throughout the year.
There are two methods for paying taxes:
Withholding
If you are an employee, your employer probably withholds income tax from your paycheck.
Income received from pensions, bonuses, commissions, gambling winnings, and other sources may also have income tax withheld from the amount you receive.
The amounts withheld are paid to the IRS on your behalf.
Estimated Tax Payments
If you do not pay taxes through withholding, or do not pay enough tax through withholding, you may need to make estimated tax payments to make up the deficit.
Generally, people who are in business for themselves pay their taxes through estimated payments.
Tax on income received from dividends, interest, rents, royalties, and capital gains is generally paid through estimated payments.
If you do not have enough taxes withheld, or you do not pay enough in estimated taxes, you may be subject to a penalty for underpaying your taxes.