Hi,
If you are transferring the shares, you would need to use the market value of the share on the date you dispose of them, to work out your gain, minus the cost of transferring the shares.
There is a calculator below to help work out your gain and allow you to report the gain using the Captial Gains Tax real time transaction service (CGTRTT).
Tax when you sell shares
If you do not use this service to report the gain, then you will be required to complete a Self Assessment tax return.
Thank you.