CGT - rental sale

[leehen]

Hello

Wonder if you can help.

I own a currently rented out property and looking to sell.

Its a little confusing hence my question.

So to run down a timeline

March 14 - bought the flat on a shared ownership basis - 50% of full value of 120,000.
July 14 - Increased lease (to 129 years) on 50% share for premium of £3160
Aug 15 - Staircased to full 100% - Property valued then at £200k so 50% being £100k. Therefore in total I paid £160,000 for the flat.
April 16 - Due to work and moving away had to rent out the property
Aug 16 - Found a new property to buy so transferred the flat to a BTL.
Sept 18 - Due to another work move selling my property bought in Aug 16 and looking to sell the BTL flat. (I'm moving into rented house for 6 months)

So my question is basically how do I work out the CGT on the flat
1 - based on the initial purchase method what is the property value I use
2 - a rough indication of CGT, as I am aware of the 18 month rule and the letting relief.
3 - If I sell my house and not the flat then go onto selling the flat later would this still be subject to CGT.


Thanks in advance.