The maths the shelf hides
Sticker prices compare two different amounts of product, and a refill system looks expensive right up until it doesn’t. These work both out. Free, no account, and nothing is saved or sent anywhere.
In the shop
The cheap box is often the expensive one
Packs hold wildly different numbers of uses, so the prices on the front compare two different amounts of product. Put both in and see what you actually pay per wash, per wipe, per squirt.
Before you commit
When does a refill system pay for itself?
The first purchase buys a bottle you keep, so the first receipt looks bad and every one after it looks good. This finds the crossover — and tells you when it is far enough out that you should buy the ordinary bottle instead.
Down to two or three
Which of these is actually the better buy?
Tap Add to Compare on up to three products in the shop and see them side by side — the price, the refill price, the sustainability claims each listing makes, and what each costs per use.
To read, not to fill in
The Green Diaries
Both calculators above started as posts. The Diaries have the arguments they came from — the workings, the caveats, and the cases where the sums say buy the ordinary bottle.