A polite way to ask is: “Please RSVP by [date] and let us know how many guests will be attending.”

More polished options

  • “Kindly RSVP by [date] and include the number of attendees.”
  • “Please respond by [date] with your attendance and total number of guests.”
  • “We kindly ask that you RSVP by [date] and indicate how many will be attending.”

Slightly warmer wording

  • “Please RSVP by [date] and share how many people will be attending with you.”
  • “Kindly let us know by [date] whether you’ll be attending and the number in your party.”

Example invite line

RSVP by June 15 and please include the number of guests attending.

If you want, I can also turn this into a formal wedding version or a casual party version.