Hello and thank you all for your replies!
This thread has thrown up so many feelings and provided so many new perspectives. It has made me confront a lot about our relationship that I already knew but have been in denial about.
It was a genuine question - at least I thought it was when I wrote it! - but I guess I know it is playing relationship games.
The thing is, for years I’ve suspected he would have forgotten but I can never hold my nerve and find out. I passive aggressively book something a few days before and then make him feel guilty that he didn’t arrange it for me, all the while not really caring about the birthday and sort of weirdly relishing having a reason to be annoyed with him.
But I just feel like I always protect him regarding my birthday, or rather protect myself from discovering/confirming if (as I suspect) I really don’t sit high on his agenda.
Every year I remind him a few weeks and then a week before (usually go out so have somewhere booked etc.) but the last few years with babies etc I have strongly suspected that without my 2/3 reminders I would get nothing (less important) and he would forget (that’s the issue). I was getting a small present usually bought on the day - ditto the card. But it’s not really about the present, it is about him showing he cares enough to make the effort just in case I was a “birthday person”.
For unknown reasons my birthday isn’t in his calendar, nor Is his mother’s which he recently forgot. I was away and reminded him but he still forgot - apparently - though I suspect he knew all day and kept putting off calling her or popping over with flowers.
And if anyone is interested we do have a kitchen wall calendar but I deliberately didn’t mark it up this year...
Anyway, thank you all for your replies. It’s good to see I’m not the only one with a crap DH. He is a real mixed bag. Though I’m sure if I posted everything about us I would get many LTBs. And you would probably be right.
But I’m not going there. Not today. This is a small corner of our relationship that I can investigate and it will probably shed light on the greater whole of our life as a couple.
Keeping quiet is an entertaining challenge for me. I have to keep his mother away as she will remind him! I won’t go mad if he forgets. I may not say anything for a few days. I really do think he has no idea as he mentioned having plans for Saturday (that he apparently told me about).
And many of you say it is game playing. And you are right.
And as one poster noticed, I come across as daft. Well yes, I am. Often. I am writhing mass of contradictions but one thing I try hard with in my relationship is to be thoughtful (and I do feel guilt when I think I’ve let someone down) (and please can I blame hot air balloon-gate on having had very little sleep last summer when I booked it and two very demanding babies.
But yes, I am daft. And probably doubly so for doing this.
My sensible side 
says tell him and have a grown up chat about it all.
My self-destructive side (and I really wanted to write “my dark passenger” then - any Dexter fans?) says don’t tell him and see what happens 
Well...I will let you know how it goes. 