DD:

The phrase "one of the partners' birthday" is in fact correct. Assume it's in the sentence: Today is one of the partners' birthday.

That sentence is grammatically equal to: Today is the birthday of one of the partners." The phrase "one of the partners" in its entirety takes the possessive when moved from behind the of to in front of the word birthday.

You would not say "Today is the birthdays of one of the partners" which is how you would have to recast the sentence "Today is one of the partners' birthdays."

When faced with a dilemma like this, it's always to try to recast the sentence for clarity.

TEd


TEd