Depending on how you've structured your big weekend, you're going to need between two and five bat mitzvah dresses or suits:
1. A bat mitzvah dress or suit for Friday night services
2. A bat mitzvah dress or suit for Saturday morning services/ lunch
3. A dress or outfit for a Saturday night party
4. An outfit for a Sunday brunch with relatives and out-of-towners
5. An outfit for a teens-only party
It's possible you've already got beautiful dresses in your closet you're psyched to wear. But a Bat Mitzvah is a once-in-a-lifetime experience so you may want to consider buying something new and special.
We suggest starting early; shops aren't exactly bursting full of bat mitzvah dresses that're both appropriately dignfied and respectful of the Torah and synagogue while still smashingly stylish.