Payroll softwares are designed with while holding rates depending on dependents/status as well as “pay period” (is it annual/bi weekly/monthly/etc. then they usually have an override amount that can just be entered in. Then it is up to the company to determine what they are going to do. If I get a year end bonus, I figure it the amount I want to have withheld from it and request that be done. I’ve had years when it has been very little based on my tax estimates, other years it has been a lot higher based on not having enough withheld during the year.