Basic CGT question for shares...?

Ciprico

..but the answer is not so easy to find..

Assuming income of 20k and CG of 29,999, (so basic tax payer), CGT is 10% of 29,999  

If income of 20k and CG 30,001 (so marginly a higher rate tax payer).

Is CGT:

30,001 x 20%
or 
(30,000 x 10%) + (1 x 20%)

If this is the case that final £1 of capital gains was a very expensive "gain", or have I understood this totally wrong 

Jeremy535897

The trigger point is £50,271 (in England and Wales) rather than £50,001, and you also have an annual capital gains tax exemption of £12,300, but the simple answer is that only the excess over basic rate is taxable at 20%. See:
https://www.gov.uk/capital-gains-tax/rates