@engineer,
It doesn't have to be a surprise - I just cannot do a conventional party at all because besides thanksgiving, I cannot plan it. I do not know when we would be available on the weekend until the last minute so planning and inviting people is out of the question.
So I thought it might be fun where I knew people would be around to have a little cake and say Happy Late Birthday with others. And maybe once I know what our schedule would be to take him out to dinner or make a special one at home - I did ask him knowing he might not want a surprise or even a party. He just said he wanted to spend it with me.
Besides that I wanted to make the day at least a little special - by dressing the house up on his day.
We talked about what we did on his 40th - we went away to a nice b&b in vermont - great foliage time of year. But as we discussed with each other - that probably will not be possible for another 6 years (this time of year is fall ball - Basket and Softball) so we have a full schedule.