Hi.Assuming that you have lived in the property for the entirety of your period of ownership of it or moved out up to 18 months ago, you can gift your share to your sister and pay no Capital Gains Tax by reason of main residence relief. Take a look at HS283 for more information on that. So long as there no cash exchange or the transfer of a mortgage in excess of £125,000, the stamp duty threshold, you should have none to pay. Take a look here for the stamp duty rules governing property transfer.You don't need to tell HMRC that you have made a gift but you should keep a record of it. So long as you live for at least seven years after making the gift, its value will not form part of your estate for Inheritance Tax purposes.I hope this helps but let me know if you have any further questions.