Although a recently qualified CTA I occasionally get a nasty surprise when I realise that a tax treatment is not as I might have assumed. Although I do a lot of research when advising clients / ensuring their compliance I do wonder where pitfalls might lurk. I wonder if people might be willing to share common pitfalls so I can add them to my list of things to be careful of?! Each time I make - or narrowly avoid - a mistake I add it to my "tax return / tax advice checklist" to try and help make sure I get things right. Examples are checking NICs where someone is both employed and self employed, or lessees not claiming CAs on finance leased assets (Thanks to BKD post).