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A person is looking through a tiny stack of bills through a magnifying loupe.
Kiersten Essenpreis for Money

If you received a tax refund that was smaller than you expected this year, chances are it’s not a random mistake. Rather, some paperwork you filled out at your job is likely to blame, and with a little digging you can figure out exactly what happened.

Currently, the average 2020 tax refund is about equal to last year's — roughly $2,800 — but every year a sizable number of taxpayers say they are surprised by the amount of their tax refund or tax bill.

Experts say one of the most likely culprits of a pint-sized refund is that you aren’t withholding enough from your paychecks for Uncle Sam. But there’s a way to avoid that unwelcome surprise: Workers have the chance to tell the government how much to withhold from their paychecks for state, federal and local taxes throughout the year using a Form W-4.

The IRS released a new version of the form at the end of 2019. A year later, the American Institute of CPAs (AICPA) found only one in four workers had updated their withholding since the new form was introduced.