Whazza22

My partner and I have a joint residential mortgage for our family home but are currently not married. I have had owned a Buy To Let property solely in my name for about 10 years but have just gifted her part ownership. We have just changed the ownership of the Buy To Let property to joint owners, resulting in my partner being added to the title deeds. She will now have a beneficial interest in the property. Stamp Duty Land Tax was paid for her share of the property when the ownership changed. Am I liable for Capital Gains Tax as I have effectively given a share of my property away? (My partner did not purchase her share, I gifted it to her). If Captial Gains Tax is due, is it based on the original purchase price and half of the current value or is it based on the share of the mortgage? Thanks in advance.