<https://creditboards.com/forums/index.php?/topic/626456-w-4-form-question/#comment-5838676>
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"Switching pay periods is not the issue. Spouse &amp; I have just gone through this when we had to make a mega-payment to the feds in May. Recent tax changes mean the old \"deduction\" system for the W-4 are obsolete.  We knew our situation was changing, so we reduced deductions from 4 to 0. But it doesn't work that way anymore. Your employer will let you set your deductions at 0 (or whatever), but now, you have to do the worksheet. If you don't, you will be underwithheld. There has been no publicity about this - it really seems to come into effect when your tax situation changes. Spouses payroll rep was unsurprised, and said a number of other employees had been through the same. Now you have to estimate everything and enter a specific dollar amount to be withheld on the W-4. OP's frustration is solid - it's wack.\n "
<https://creditboards.com/forums/index.php?/topic/626456-w-4-form-question/&tab=comments#comment-5838711>