You could create 3 different fields (Month, Day, and Year), and just leave the Year field blank when you don’t know what it is.

Short of any other ideas, I may enter the month and day in fields, then use them along with the age to calculate the year and enter all of them in the date field.

I have this same question but for two different scenarios.

I actually do something similar to this kids case study but in my case, with actors, to track their ages for roles 😉 but I also need it for gardening (I don't want to have to keep putting in the same ballpark seasonal dates of when to sow, plant indoors, transplant outdoors, etc.) and/or say film festivals and awards shows (annual events that are ballpark right around the same time - and I can adjust annually as they shift a weekend or two). 

I can certainly split into three columns (but then I lose the ability to do the calendar subscription - which is very handy) or add a column and a formula to add a year but... just thought I'd see if there were any easier other ways or brilliant ideas?

Just wanted to chime in and mention a desire for the same thing, particularly with a focus on the ability to have it show on the calendar each year. We track birthdays for employees but don't want the year visible, just the month/date.

Alternatively, is there perhaps a formula that would let us have a full date field and then only pull the month/day into a separate field? We could hide the full date and only have visibility on the month/day and that would meet the need in our situation.

@Mouser-IB-Admin - Having separate columns for Month, Day and Year SHOULD solve this for you.

You could then use a formula to concatenate just the Month and Day for your calendar subscription. 😉  

That's the suggestion I keep seeing in other similar posts too, so it may  unfortunately be the only way to do it.. Thanks!