The reason an expiring discount beats a larger permanent one

Fifteen per cent off, ending Sunday, converts better than twenty per cent off with no end date. The larger saving is available whenever the customer wants it, and that availability is the problem: nothing about it makes today different from next month.

What everyone sees

Discount size is treated as the lever, so a larger reduction should always win. Under that model the deadline is a detail. The observed result is that the deadline is doing more work than five percentage points, which looks irrational until postponement is counted as a cost.

What is actually happening

Present bias and procrastination research, following Laibson and O’Donoghue and Rabin, shows that tasks with no deadline are deferred repeatedly even when the intention is genuine. Nickerson and Rogers found that prompting people to specify when and how they would act raised follow-through substantially. A deadline performs the same function externally: it converts an open intention into something with a date, which is the form actions actually take.

Why it stays hidden

The mechanism hides because the customer’s intention is real throughout. Someone who plans to buy at twenty per cent off next month is not lying and does not experience themselves as declining. The lost purchase never appears as a refusal in any record, and the seller sees only that the permanent discount underperformed, which is easy to attribute to the number rather than to the missing date.