RE: Self assessment30 Jan 2021 12:09
If this is in a trading account then it is usually 'first bought, first sold', so you calculate in that order
So say you bought 2* £10k at 100 and 125, so you have 10,000 and 8,000 shares bought
... price now is 150 and you sell
15,000 shares. Your declared profit would : 10,000 * (150-100) + 5,000 * (150-125) = £5,000 + £1,250
8,000 shares - profit is 8,000 * (150-100) = £4,000
In a SIPP or ISA there is no declaration as they are tax free for CG