That's my thinking too.  There's no way I could provide details of every transaction I've made over the last 4 years, especially bct to alts to btc, etc.  And also considering that there's now no way for me to access any records from Mt.Gox.  So presumably the tax authorities (HMRC in UK) would reasonably accept the "$out minus $in" figure. That's my hope anyway.  But still, paying Capital Gains Tax on crypto profits would grate, a lot.

Just wondering if anyone here has yet made a CGT return to HMRC and how it was dealt with? They're massively under-staffed (up to 45 minute waiting time when phoning them, if you manage to get through at all).  My guess is that they would accept pretty much whatever method you decide to use (i.e. a "$out minus $in" figure) as long as it seems justifiable, and they would only rarely investigate further to see if your figures are accurate, in the way that usually just accept at face value most people's regular self-assessed tax returns. I doubt they have the resources to do anything further.

Has anyone here actually dealt with HMRC yet regarding btc profits? It would be interesting to hear about your experiences.