My wife and I have just been doing our 2017-2018 UK tax self-assessments online (yes I know... leaving it to the last minute... they are all done now though).
As during that tax year my income was below the personal allowance while she was in the basic rate range, I wanted to take advantage of the "Marriage Allowance" option of transferring some (£1,190) of my "unused" personal allowance to her.
While I was going through the self-assessment process, it did actually give me the option of doing this (I forget the exact details, but I do remember it asked for my wife's national insurance number). However while going through my wife's self-assessment (which we did second) there seemed to be no point at which she could mention such a transfer had taken place or was being claimed and there was no sign the transferred personal allowance had affected her tax calculation.
How is this actually supposed to work? I can imagine it might take a while for the transfer to register in HMRC's systems... but then would she just find herself credited with any overpaid tax, or will something need amending/resubmitting once her personal allowance has actually updated? Or did we miss some point where she should have claimed it?