Shares sold to cover the tax at vest are a disposal

The rule

When RSUs vest, the whole award becomes yours before anything happens to pay the tax on it. Where some of the shares are then sold on the vest day to cover that tax ("sell to cover"), HMRC treats the whole award as acquired first — every share is yours for a moment — and the shares sold to cover the tax are a disposal of their own, separate from the Income Tax already charged on the vest itself (HMRC guidance, Employment Related Securities Bulletin 63, January 2026; ERSM140095).

The same-day rule, and why the gain is usually nil

Capital Gains Tax matches a disposal against an acquisition of the same shares on the same day before it looks anywhere else (Taxation of Chargeable Gains Act 1992 s105). A sell-to-cover sale happens on the vest date, the same day the shares were acquired, so it is matched against that acquisition. The proceeds and the base cost are both close to market value on the vest date, so the gain is usually nil, or a small loss equal to the broker's dealing fee.

It still goes on SA108

A disposal with a nil gain is still a disposal. It counts towards box 23 (number of disposals) and box 24 (disposal proceeds), even though it adds nothing to box 26 (gains before losses). Disposals of the same class of share in the same company on the same day count as a single entry in box 23, so a sell-to-cover sale alongside a separate voluntary sale of the same shares on the same day is one line, not two.

Whether the Capital Gains Tax summary pages are needed at all turns on proceeds, not gain: they are compulsory once total disposal proceeds for the year exceed £50,000, or gains before losses exceed £3,000. A sell-to-cover sale's proceeds count towards that £50,000 figure even though its own gain is close to nil — on a return with no other disposal at all, it can be the reason the pages are needed.