Just remember that overwithholding by the federal government results in a tax refund of our own money when we file our taxes, and we are so glad to get that money back (an interest free loan to the IRS for most of the year!)  The best tax planning strategy is to owe taxes to the IRS when you file and don’t pay the dreaded underpayment penalty (meaning you only pay in enough tax to avoid the penalty and you keep the float.)  This takes more planning but long term you can come out ahead.