Capital gains tax on a property sold in Luxembourg

Hello, I wonder if you can help? My mum is in the process of selling her apartment in Luxembourg and will be relocating back to Britain in April. The apartment is her sole residence in Luxembourg and she’s lived there for over five years, Please could you advise whether capital gains tax would be charged on the sale of her apartment if the completion date is after the date she moves back to the UK? With many thanks and best wishes

Hi,
If you mum is resident in the UK when the disposal is completed, then, their could be a UK Capital Gains tax liability.  
Any gain is worked out using UK rules.  All figures used in any calculations must be converted to pounds sterling, using a just and reasonable exchange rate that applied at the time of acquisition and disposal.  As this is a foreign property disposal, it would be declared in a Self Assessment tax return.  Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal.  
For your convenience, there are exchange rates at: https://webarchive.nationalarchives.gov.uk/ukgwa/20231016190054/
Exchange rates from HMRC in CSV and XML format
and for older rates at
https://webarchive.nationalarchives.gov.uk/ukgwa/20100602124114/Exchange rates from HMRC in CSV and XML format.  
You are free to use any of the supplied rates or one of your own choosing.  
There is a calculator at Tax when you sell property to help you work out the gain.  
As the property was your mums main residence for a period of time, she will be able to claim privare residence relief and include this in the tax calculation.  
Please have a look at: HS283 Private Residence Relief (2024) for more information.
Thank you.