Cost per use
What your routine actually costs per application and per year
- Free, no sign-up
- Runs in your browser
Your routine
Size, price, and how much you actually use. Everything stays in this browser, so it is still here when you come back.
Add a product to see what it costs you.
Nothing is sent anywhere — the figures stay in this browser.
Compare two products
The decision you actually make in a shop: two bottles, two prices, two very different sizes. Cost per use settles it; the shelf price often does not.
Fill in size, price and amount for both products to compare them.
What people use this for
- Your routine crept up in price. Nobody buys an expensive routine on purpose. It accumulates one replacement at a time.
- You are deciding between two products. Price on the shelf is not cost. A larger bottle used sparingly often wins by a wide margin.
- You want to cut without losing results. Seeing annual spend per product makes it obvious which one to replace first.
Why cost per use is the number that matters
Shelf price tells you almost nothing on its own, because products differ enormously in how long they last. A cleanser used twice daily at 2 ml a time empties a 200 ml bottle in about seven weeks. A retinoid used on a pea-sized amount three nights a week can make 30 ml last most of a year. Those two can carry the same price tag and differ by a factor of ten in what they actually cost you.
The calculator works out how many applications each container holds from its size and your typical amount, divides the price by that, and then projects forward using how often you actually use it. The result is a cost per application and an annual figure per product, which is the number that makes a routine comparable to anything else you spend money on.
Getting the amounts roughly right
The defaults come from commonly cited application amounts: around 2 ml for a cleanser, 1 ml for a toner, a pea-sized 0.25 ml for a retinoid, and roughly 1.2 ml of sunscreen for a face and neck at the density dermatologists recommend. You can override any of them, and you should if you know you use more.
Sunscreen is the one worth being honest about. Most people apply between a quarter and a half of the recommended amount, which makes their sunscreen look cheap and their protection considerably lower than the number on the bottle. If you correct your usage upward, the annual cost rises accordingly — that is the real price of using it properly, and it is useful to see.
What the totals leave out
The calculation assumes you finish what you buy. In practice a lot of skincare is abandoned part-used or expires after opening, and both make the true cost higher than any arithmetic here. If you routinely replace things before they run out, treat the annual figure as a floor.
It also has nothing to say about whether a product is worth its price. Cost per use is a measure of efficiency, not of value: an expensive product that solves your problem can easily be worth more than a cheap one that does nothing. Use this to find the places where you are paying a premium for no reason, not to decide that the cheapest routine is the best one.
Frequently asked questions
Why does cost per use matter more than price?
Because products last wildly different lengths of time. A cleanser used twice daily empties in weeks; a retinoid used three nights a week on a pea-sized amount can last most of a year. Two products at the same price can differ tenfold in what they actually cost you.
Where do the default amounts come from?
Commonly cited application amounts — roughly 2 ml for a cleanser, a pea-sized 0.25 ml for a retinoid, and 1.2 ml of sunscreen for a face and neck at the density it is tested at. Override any of them if you know you use more.
Does this include products I abandon?
No. The maths assumes you finish what you buy. A lot of skincare is abandoned part-used or expires after opening, so treat the annual figure as a floor rather than a ceiling. Where one container would last more than a year, the tool flags it, because that is usually money spent on product that will be thrown away.
Does a lower cost per use mean a better product?
No. This measures efficiency, not value. An expensive product that solves your problem is worth more than a cheap one that does nothing — use this to find where you are paying a premium for no reason.
Is my routine saved anywhere?
Only in this browser, using local storage on your own device. Nothing is uploaded, there is no account, and clearing the routine removes it. Open the page on a different device and you will start from an empty list.
How does the comparison decide a winner?
It divides each product's price by the number of applications its container holds, so a big bottle used generously can easily lose to a small one used sparingly. It also gives the break-even price: what the losing product would have to cost, at its own size and dose, to match the other.