CGT calculating

Could you please advise the method used to calculate the gain in the following circumstances : After the initial investment into a unit trust fund, regular payments of £50 per month have been made over a period of 10 years. This would mean 120 transactions. As these purchases inevitably would have been made at varying costs how do I calculate the gain to be declared on sale ? Thank you

Hi,

You can see guidance here:

CG51575 - Share identification rules for capital gains tax from 6.4.2008: the Section 104 holding in detail

Thank you.