I don't remember what all the limits are but the first time you underpay beyond a certain amount the government looks the other way but the second+ time you hav

I don't remember what all the limits are but the first time you underpay beyond a certain amount the government looks the other way but the second+ time you have to pay penalties. Penalties for a situation wholly in control of the government. They wrote the withholding tables your employer is abiding by to withhold _not enough_ to avoid you having a penalty at the end of the year. Although I suspect this only matters to FANG where the changes to withholding from the Tax Cuts & Jobs Act meant you had to modify the supplemental withholding rates so you wouldn't get penalized.