Chris

I realise now my example doesn't really show my issue properly as I could still file self-assessment for the £1000 loss in 24/25. Instead imagine that occurred in 23/24 where self assessment period has since closed.

As I understand it, you can claim past losses up to 4 years after the end of the tax year that you disposed of the asset. so for example: - 24/25 disposed of asset with a **-£1000** loss - 25/26 disposed of asset with a **+£10000** profit My understanding is that the losses made in previous tax years carry forward and mean that you only pay CGT on the overall profit. i.e.: £10000 - £1000 = **£9000** (and then you deduct from that the tax-free CGT allowance of £3000, so actually only £6000 is taxable) My question is, should one report the losses in advance of filing self-assessment for the current year? i.e., report the losses via a letter to HMRC, then later file the self-assessment at the end of 25/26 declaring the £10000 profit (with no reference to previous losses), and then HMRC will see the past losses in your records unprompted, and bill you accordingly? Do you declare/reference the previous years losses within self-assessment for the year in which you want to make use of them? Second question: is there a template for the letter for declaring past losses? I'm not sure how much detail is expected. Thanks!