Again, that is a context thing. If you are talking about your sons upcoming birthday that would be the nearest one. I rarely see people referring to events by the exact date if it isn't some momentous occasion (9/11 ... but what year?), or to plan something.

If you typically refer to all days of the year past when the upcoming one is very close then you'd probably make that plain with some note on context. If not you might find yourself with an unscheduled party on your hands :)