Query on CGT for non-residental property sale

My wife and I have lived in Australia since 2008 and will hopefully be selling our original residence in the UK shortly (that we owned and lived in from 2000 to 2008). I understand CGT is applicable on the gain from 5th April 2015 but have a couple of simple questions. 1. When I've used the HMRC calculator for CGT it doesn't ask about joint ownership so appears to calculate the CGT based on sole ownership. Is it acceptable to use 50% values across all the amounts to provide a per-person CGT amount? 2. I've seen references to Principle Private Residence Relief "for the final 9 months". To be honest I don't really understand what this phrasing means. It's about 115 months from 5th April 2015 to present - so does this mean we can deduct a fraction of the gain that aligns to the total months (i.e. 9/115 = 7.826%)? Or is there some other intepretation? Thanks! Dave

Hi,
The guidance at CG73700 onwards advises that you use the rebased value of the property at 5 April 2015, when calculating your capital gains:  
CG73700 - Non-Resident Capital Gains Tax (NRCGT) - Disposals from 6 April 2015 to 5 April 2019
Private residence relief (PRR) can be claimed for the period that the property was your main residence. Guidance on calculating PRR can be found here:
Private Residence Relief (Self Assessment helpsheet HS283) 
There is a capital gains calculator to help you work out if there is a gain below:
Tax when you sell property
If there is, you can move on to the next section to register for a capital gains account, report and pay the capital gains tax due within 60 days of the completion date.  
If you are unable to verify your identity, you will need to contact our Self Assesment team for further advice.
Self Assessment: general enquiries
Thank you.