Question:
Are we allowed to celebrate birthday in bein hametzarim At home with family ?
Answer:
During the three weeks it is permitted, but during the nine days it isn’t a correct thing to do, as we don’t have parties during the nine days. It should be pushed off until after the nine (10) days.
Sources:
Kovetz Halachos ( R. S. Kaminetzsky shlit”a) Bein Hamitzarim 10-8.