Hi,
When you acquired your second property, you should have confirmed within 2 years which property is to be treated as the main residence for Private Residence Relief purposes. You can see guidance here:
CG64495 - Private residence relief: only or main residence: two or more residences: time limit for nominating
Where no nomination is made, relief will be available in respect of the residence which is the main residence as a matter of fact; the deemed residence is not automatically relieved. Yoiu can see the guidance here:
CG64545 - Private residence relief: two or more residences: no valid notice made
Private Residence relief, where it is due, is used to reduce the capital gain arsising from the property disposal. Guidance on Private Residence Rrelief can be found here:
HS283 Private Residence Relief (2024)
There is a capital gains tax liablity calculator below from which you can elect to register for a capital gains account and report and pay any Capital Gains Tax due.
Tax when you sell property
Thank you.