Hi Iris Look,
Add together the aquisition costs
1 - 50% of the acquisition cost in 2013 and
2 - 50% of the acquisition cost in 2019.
Deduct this total including your costs such as stamp duty, solicitors fees etc.
If you are left with a positive figure, this is the amount of gain and if a negative figure, the loss.
In addition to this, you also have private residence relief that you can set against the gain.
HS283 Private Residence Relief (2023)
Thank you.