1 Most US employee share schemes are non-qualifying as far as HMRC in the UK is concerned. That means that the difference between what you pay for the shares, if anything, and the price when they vest is chargeable to income tax and national insurance contributions. There is no way around that, that's simply the way they are taxed. Most people don't have the cash to pay the tax when the share vest so its normal for the tax and nic to be covered by selling some of the shares. If you held on to them and paid the tax and nic from your own resources, their cost for CGT purposes would be the sum of what you paid for them and the amount on which you paid income tax and nic. If at some stage in the future you sold them for more than the CGT cost, then you may have CGT to pay.
If you sell shares at below the amount you paid for them, ie the vesting price was lower than what you paid for them, then youn will have no income tax or nic liability.
2 That's correct.
3 That's correct.
4 If the transaction is run through the payroll, then the income (the gain on the shares) will be included in your tax year end P60 so it is simply reported as employment income. Any capital gain, as mentioned by you in 2 above, would be reported in the capital gains pages of the tax return.
If shares vest after you leave the employer, the gain will still be suibjected to income tax. I tend to use boxes 3 and 6 in the share schemes section on page Ai2 of the SA101 pages here for clients.
I hope this helps but let me know if you have any further questions.
If the disposal proceeds of all your capital transactions in any one tax year exceed four times the annual CGT exemption (£44,400 (4 x £11,100)), the transactions have to be reported regardless. You will need to claim losses by reporting them to HMRC as if you don't do that within four years of the end of the tax year in which net losses were incurred, you lose the right to use them.
You can make £11,100 of gains in the 2016/17 tax year and pay no CGT. If your total proceeds of all capital transactions is £44,400 or more, you have to report them whether you make gains or not. Look under the heading "How do I report capital gains to HMRC?" here. If the total proceeds are less than £44,400 but you make gains in excess of the annual exemption, you have to report them. Net losses for a tax year should be reported to avoid losing the right to use them.
The CGT and the income tax liabilities on your RSU's are separate from one another.