I don't know about you, but I have almost all the important dates for birthdays, anniversaries etc. memorised and very rarely forget one (I even remember quite a few birthday dates from my class mates in the elementary school).
S. however is quite the opposite. He has the most important dates in mind (his birthday :D, my birthday, his mother's and sister's birthday and our anniversary) and so far hasn't forgotten my birthday (which is very unlikely to happen, since it's two days after his b-day). But that's about it for dates he has memorised. So one day, when looking at my pretty month stamps by LoraBailora, I had the idea of making a really simple and easy (almost pocket-sized) birthday calendar.
I shared the full tutorial on the LoraBailora blog a few weeks ago. Of course you could also change the size of the calendar and make it even bigger so you can hang it up, or even smaller so it fits in a bag and you can take it with you wherever you go.