Why is my Social Security tax so high on my vested shares?

[safox]

Hi everyone,

I just had my first major stock vest at work, and I was shocked to see how much was taken out for Social Security and Medicare. My neighbor, who is a tax consultant, mentioned that since these are considered supplemental wages, the FICA hit happens all at once.

I've been trying to find a reliable rsu fica withholding calculator to see if my company's payroll department did the math correctly.

It's a bit confusing because I'm nearing the annual earnings cap, and I don't want to overpay. Does anyone have a preferred rsu fica withholding calculator?

Thanks in advance.