Quick answer
Save-the-dates 8-10 months out, invitations 8 weeks out, RSVP deadline 3-4 weeks before the wedding, one reminder at each stage, final numbers to the venue a week after the deadline.
Save-the-dates: 8-10 months
Earlier for summer and holiday-weekend dates, earlier again if most guests are travelling. A save-the-date is not an invitation and should not carry an RSVP — its only job is to protect the date in people's calendars.
Send it only to people you are certain about. Withdrawing a save-the-date is a conversation nobody enjoys.
Invitations: 8 weeks
Eight weeks is long enough for guests to arrange childcare and travel, and short enough that the wedding feels real rather than theoretical. Twelve weeks for destination weddings; six is workable for a small local wedding where everyone already knows.
First reminder: 3 weeks after the invitation
Non-responders only, gently framed. At three weeks people are not late — they are distracted, and the reminder is genuinely helpful rather than pointed.
RSVP deadline: 3-4 weeks before the day
Set it from your caterer's actual cutoff minus a week. Publish the same date everywhere, and say it as a date rather than as "as soon as possible".
Deadline reminder: 3-5 days before
Direct and short, with the date and the link. This is the message that converts most of the remaining pending list.
Personal chase: the days after the deadline
Whoever is still silent gets a message or a call from you, not another email from a platform. The list is usually short enough to work through in an evening, and half of them will apologise and reply immediately.
Final numbers: about a week after the deadline
Headcount and dietary requirements to the caterer, per-part numbers to the venue if the day has separate elements. Send the list as an export rather than as a screenshot of a dashboard.
Seating: the last fortnight
Only once the numbers are stable. Seating built earlier gets rebuilt, and rebuilding a seating plan is the single most tedious task in wedding planning.
If you are running behind
The compressible parts are the gaps between stages, not the stages themselves. Even at four weeks' notice, the order holds: invite, remind, deadline, chase, confirm. What you cannot skip is telling guests a specific date by which you need to know.