How long should a promotion run?

Long enough to see a pattern, short enough that customers do not build it into their expectations. A few weeks is usually right.

Can I just run one permanently?

You can, and then it is not a promotion, it is your pricing. Customers adjust and the lift disappears while the cost does not.

Should you run a promotion?

Run one when you can name the behaviour you want to change and can bound it in time. Promotions fire without a customer choosing them, which makes them powerful and makes them the easiest way to give margin to people who were coming anyway.

A promotion is a rule that fires automatically when a customer is scanned. Nobody buys one, which is exactly what makes it both effective and easy to overspend on.

Start with the behaviour, not the offer

Name what you want to change. A quiet Tuesday afternoon. A new product nobody is trying. Regulars who drift in February.

If you cannot name it, you are about to discount customers you already had.

Do the arithmetic before, not after

Work out what it costs if everybody who qualifies takes it up. That worst case is the number that matters, because a promotion that fires automatically has no natural ceiling other than your customer count.

Bound it

A start date and an end date, always. Open-ended promotions are the single most reliable way to lose money slowly on a loyalty platform.

The measurement problem

The hard part is knowing whether it worked. Sales during a promotion are not the test, because some of those customers were coming regardless.

Compare against the same period without it where you can, or against a comparable group. If you cannot, be honest that you are going on judgement rather than evidence. That is a fair choice, as long as you know that is what you are doing.

The pattern that usually works

Narrow, time-bounded, aimed at a specific slot. Double stamps on Tuesdays in February, not double stamps forever.

The pattern that usually does not

A permanent promotion layered on top of a loyalty programme. Customers absorb it into their expectations within weeks, so the lift goes away and the cost stays.