RSU vested: both income and taxes already in W2

If the company is public, the value of your RSU is categorized as short term gain (income) on the day you received it.  You owe tax on that amount.  You will owe tax at your total tax rate, and it should be paid with your quarterly estimate.  Here's where it gets hard to do.  The company you work for has decided on a policy of what percentage of your RSU is withheld for taxes.   You don't have a choice in the matter.  But you still owe the tax.  So say your income is 50,000, and you get an RSU that's worth 50,000 at vesting, your tax rate went from say 23% up to 32%.  You owe the tax difference on the first 50,000 income.  OK, it gets harder.  RSUs are often granted more than once per year.  So you should look at your RSU grant schedule, assume you're going to receive it all, and estimate your tax accordingly so you don't end up with a whopping payment and potential penalty.  If you don't do this, TT will calculate a penalty for you.  You can get your grant schedule from your fiance department.  The difficulty isn't over yet.  The company has a policy on how much to withhold.    I know one company that decided on 33%, and one company that decided o 42%.  Neither number will be right for anyone granted an RSU.  You have to do your own.   If you are over-withheld, you will get the money back from the IRS in your refund check.  If you are over-withheld too much, there will be a penalty, so don't forget you can adjust your withholding amount so it comes out pretty close.  If you are under-withheld, you will have to write a check when you file your taxes, and again, TT will calculate your penalty.  And one commonly misunderstood concept is that your broker will *not* issue a 1099 for the shares withheld, since they are not sold, but their value has been dumped into your W2 income and tax buckets by your company.  Your broker will never see those shares. You can get the percentages for each bucket from your finance department, but really, you don't need to care about that level of detail.  Unless you work in the tax squad in your company's finance department.  And don't worry about your company, because they are getting a great deal on this whole thing.  The money they dump into your tax bucket comes from profits, which lowers their taxes, and the shares that are withheld get dumped into the stock reserves bucket, which of course isn't taxed because those shares aren't sold.  But they can be used for future RSUs, ESPPs, grants, loan collateral, lots of things just so long as they don't get sold.  And don't worry about future sales of your leftover shares at your broker's.  Your broker knows the value of those shares was the value when you received the grant, and the tax is paid on that value already, so if the stock goes up, you simply have to pay the tax on the sale value less the value when you received the shares.  You can use TT for that; as well.  Where this gets complicated is with FIFO, the shares you sell are from the oldest bunch of stocks you put into your account, which may be years ago, and you have to come up with all that tax money.  It gets even more complicated when you change brokers, because the new broker isn't going to have a clue as to what the value of the stock was when you got it, so (I believe this to be the case but needs checking) they assign a value of 0.   I only changed brokers once in my life, many years ago, and had the first of my 5 heart attacks when I opened that 1099......So keep records, and understand the paper you're keeping.  I will stake my professional reputation (such as it is) on two things:  One is that you will never see a 1099 from your broker covering RSU shares withheld for taxes, and if you see the total number of RSU shares granted being received by your broke on your vesting day, you can rest assured that your CFO is not long for that position

In case anyone was in my situation. My RSU broker did send me a 1099-B for sell-to-cover stocks and indicated the cost basis was 0.  After a lot of research, I realized they also included a supplemental page with an adjusted cost-basis which is what is needed to input (not as the original cost basis, but as an adjusted cost basis) bringing the short-term gains to 0.