The IRS urges everyone who works as an employee and has income from other sources to perform a Paycheck Checkup. This includes income from sharing economy activities, interest, dividends, self-employment, capital gains, or prizes and awards. A Paycheck Checkup can help you avoid receiving a lower refund, an unexpected tax bill or underpayment penalty when you file your tax return next year. You can do a checkup using the IRS Withholding Calculator or Publication 505. This is especially important in 2018 due to tax changes taking effect this year. You can pay taxes throughout the year anytime.