1. Key points

  • Withholding too much leads to a refund; too little can mean a bill and possibly a penalty.
  • The IRS Tax Withholding Estimator helps you set your W-4.
  • Life changes (marriage, a new job, a side gig) are good times to recheck.
  • A refund is your own money returned, not a bonus.

2. Side income

Freelance or gig income usually has no withholding, so you may need to make estimated tax payments.