How long should a promotion run?
Long enough to do its job, and no longer. There is no universal best length: the right window is set by what you want the promotion to achieve, not by a calendar habit or whatever you ran last time. A short run concentrates attention and creates urgency, while a longer run trades some of that urgency for reach and repeat participation. Decide the goal first, then pick the shortest window that lets it happen.
When is a shorter promotion the right call?
When the point is a spike, not a habit. A tight window, from a few days to a couple of weeks, tells people to act now, which suits a product launch, a seasonal moment, or a single clear push. The cost is reach: anyone who misses the window is gone, and there is little room for word of mouth to build. Keep it short when urgency is the whole idea.
When does a longer promotion make more sense?
When you want reach and a repeatable habit rather than a single burst. A longer run, from several weeks up to a season, gives more people the chance to find it, lets participation spread through word of mouth, and, if the mechanic rewards coming back, turns a one-time entry into a routine worth returning to. The risk is a flat middle, where a promotion sags between the excitement of launch and the pull of the deadline. That stretch is where most long promotions are won or lost.
How do you stop a long promotion going flat?
Give people a reason to return, not just one prize at the end. Milestones, rewards that refresh, or a mechanic that pays off each time someone takes part keep the middle alive, so the length works for you instead of against you. This is the difference between a promotion people enter once and one they come back to after it ends.
Is there a simple rule for setting the length?
Match the length to the goal, then end while people still want more. Pick the shortest window that lets the goal happen: a spike wants days or a week or two, reach and habit want weeks to a season. Set the end date before you launch, publish it, and hold to it, because a visible deadline is part of what makes people act. Stopping while demand is still live leaves the audience ready for whatever you run next.