Report claim capital loss for 2019/20

I have made £24000 gain in 2019/20, and £15000 loss. My understanding is that I can report £3000 loss for that year, as 15000 - (24000 - 12000) = 3000 Can I still report this loss or it is too late?

Hi Flybird2023,
You have 4 years after the end of the tax year in question, to claim losses.  
If you are required to complete a tax return, the losses would be claimed in SA108 in the tax year they arise, after which it is too late.  
If you do not need to complete a tax return, then the losses must be claimed in writing and submitting with supporting evidence.
Thank you.