In box number 12, a 5 ml serum. On the full-size listing, the same one in 30 ml: the miniature holds a sixth of the contents. The ratio isn't up for debate — what's up for debate is the price you set against it. And that's where December's boxes stop being a bit of festive magic and turn into an arithmetic exercise.

What's actually in the boxes

Most beauty advent calendars don't contain twenty-four full-size products: they contain twenty-four trial sizes, and the gap in size is more brutal than you'd think. A full serum often sits around 30 ml, sometimes 50; the miniature drops to 5 or 7. A day cream is usually sold in 50 ml, the box version offers 10 or 15. Perfume often goes from the 50 ml bottle to the 2 ml vial, which fits in the palm of your hand and won't see you through the summer.

A 5 ml miniature bottle beside the 30 ml full size, and a 2 ml vial next to the 50 ml bottle
Five millilitres in the box, thirty on the shelf

The habit to get into is crushingly mundane: look at the volume, not the name. It's tedious — often the box doesn't list the sizes, so you have to dig into the online listing, sometimes box by box. I haven't opened every set released this year, and I doubt many people have. So when no information is forthcoming, assume you're buying a pretty box with a surprise inside: that's not a bad purchase, it's a different purchase.

The price-per-millilitre acid test

Do the maths once and you won't forget it. Take a serum at £20 for 30 ml — that works out at 67p a millilitre; the 5 ml miniature is therefore worth, at the full-size price, around £3.30. Put twelve of those minis in a £39 box and you've paid the normal rate for the contents, with some cardboard thrown in.

Twelve serum miniatures arranged in a grid in front of a full 30 ml bottle
Twelve minis, one full size: the arithmetic of the box

The arithmetic has its limits, and they need saying. Plenty of calendars slip one or two full sizes into the last boxes, which changes things — provided you check which ones and actually want them. A 2 ml perfume isn't assessed like a skincare product: you don't buy it by the litre, you try it. For everything else, the division stays ruthless.

Out of twenty-four, how many will last?

The sorting isn't by brand, it's by product type. A miniature mascara gets used up, and it's arguably the best travel candidate since you bin it after a few months anyway. A lipstick in a shade that isn't yours, on the other hand, will never see the bottom of the tube. And as for the third scented shower gel in the box — honestly, what's the point?

A hand placing a miniature mascara into a cotton pouch, among eight sorted miniatures
Sorting the minis, between basket and cupboard

The rest ends up in your cupboard. A 10 ml exfoliant can be two or three applications: half a week of real life. A mini cleansing oil often gets knocked over faster than it gets finished. In practice — and this is an editorial marker, not a statistic — you'll often find eight to ten genuinely usable products out of twenty-four. Fewer still if your routine is already locked down or your skin doesn't like change.

The eight-box test: before you buy, open the contents list and note every product you'd buy in full size at the normal price. Eight out of twenty-four and the calendar stands up. Five, and you're mainly paying for a pretty box — which isn't forbidden, as long as you know it.

Glass, refills, cardboard

Third check, less obvious: what the containers are made of. A glass jar recycles cleanly, but it's heavy to transport, and a thick glass miniature isn't automatically more virtuous than a light tube. The real question isn't "glass or plastic", it's "how long do I keep this container".

A flexible refill fitted into a glass face-cream pot, the lid resting beside it
The refill counts as much as the cream pot

Refills are worth a look, on one condition: that they exist for the full size, not the miniature. A calendar whose products can be rebought as refills has some class; a calendar whose pretty minis are never refillable is a catalogue of samples. Count refillable containers the way you count products: it only counts for something if the range follows through.

Budget

In the UK, by November, you'll see boxes at £30 to £45 in pharmacies and supermarkets, more elaborate sets at £60 to £120 in beauty retailers, and gift sets from skincare houses climbing from £150 to £350. These aren't exact prices, they're the most common orders of magnitude: the city, the retailer and whether there's a full size in the box can triple the bill.

Where to look? Supermarkets and pharmacies for the lower prices, beauty retailers and the brand's own site for the more considered line-ups — and there, read the contents list before you hit confirm, not after.

At the bottom of it, the only question worth asking is the one you ask in front of a box of chocolates: are you going to eat the lot, or give half of it away? A beauty advent calendar is a good buy when you know what you're after — minis to try, a full size to treat yourself, containers you'll keep. The rest is cardboard.