There are many different ways to word your reply by date on your response card. Typically you would request an RSVP about 4 weeks in advance of the wedding, but check with your venue and caterer in case they need more notice. Here are a few suggestions we have for wording:

The favor of a response is requested by the First of July (most formal)
The favor of your reply is requested by the First of July
Kindly reply before the First of July
Please respond by the July 1, 2019
RSVP by the 1st of July, 2019