RSUs are a form of compensation that is generally taxed at the time of vesting, whereas employee stock options are usually taxed at the time of option exercise. The employer is required to withhold taxes as soon as the RSUs become vested.However, if you made an IRC section 83(b) election, you will be taxed and have withholding at the time the stock is transferred to you.
When this stock vests,you, as an employee, have 3 choices ; choice 1.A same day sale of all the stock. You receive the cash left over after subtracting withholdings; choice 2.Sell to cover. The employer sells just enough shares to cover the tax withholding and you keep the remaining shares and can sell them whenever you want;choice 3.Cash transfer. You must come up with the cash to cover the required tax withholding amount. If you pay over the amount of cash to cover withholding, then all of the shares belong to you and they can be sold whenever you want. In all three choices above, your employer will include the total value of the vested RSU shares in Box 1 of your W-2 along with the amount of your normal wages. The employer is also required to withhold both federal and state taxes. This withholding will also be reflected on your W-2 along with your normal withholding. Your basis in all vested shares you receive is the amount included on your W-2 as income plus any amount you had to pay for the shares. For choces #1 and #2 above, you will receive a Form 1099-B reporting the total sales proceeds for the number of shares sold. You may receive a 1099-B for option #3 if you sold any of the shares during the current tax year.
The entry for Cost or Other Basis will be the amount included in income for the number of shares sold, as well as any amount per share you had to pay. For options #1 and #2 above, your entry for cost will generally be the same as the amount reported as sales proceeds. Since the stock is sold on the same day it vested, all income is reported on your W-2, so no income (gain/loss) should be reported when entering the 1099-B information. Other 1099-B information must still be reported and is transmitted to the IRS with your return. You may need to talk with your employer or plan administrator to determine how your stock was transferred and what amounts are reported on your W-2.