Why per day pricing beats per month

Ninety a month, or three a day. The same subscription, the same annual total, and the second version is the one printed on the poster. It is also the version buyers describe as cheap, while the first is described as a commitment.

What everyone sees

The choice looks like a presentation preference — a smaller number is friendlier, and everybody knows the two figures amount to the same thing. Since the arithmetic is trivial and the period is stated, the assumption is that anyone paying attention converts one into the other and is unaffected.

What is actually happening

The active variable is the unit, not the period. Burson, Larrick and Lynch showed that expanding or contracting the scale a quantity is expressed on changes how large differences appear, even when the quantities are identical. Pandelaere, Briers and Lembregts documented the same unit effect: a change expressed in a finer unit is judged bigger. Bagchi and Davis found that whichever figure is presented first anchors the evaluation. A per-day price wins twice — the number is small, and it is compared against small daily outlays rather than against monthly bills.

Why it stays hidden

The conversion is available and almost never performed. Performing it requires treating the printed frame as a choice rather than a fact, and nothing on the poster suggests that it is. The buyer also has no rival daily figure to set beside it, since competitors quote monthly, so the cheapest-looking unit is the one that escapes comparison.