Product Usage Duration Calculator (how long toothpaste, shampoo or cream lasts)

Understanding the product usage duration calculator — concept and principle

This calculator works out how long a container of toothpaste, shampoo, cream or any product lasts at your rate of use, when it will run out, how many you need a year and what it costs per day. It helps with budgeting, comparing pack sizes and stocking up before travel.

Uses ÷ uses per day: with the default inputs the result is Dec 30, 2026 (runs out · $0.09 a day).

How it is calculated

Uses per container = size ÷ amount per use.
Days it lasts = uses ÷ uses per day; weeks = days ÷ 7.
Run-out date = opening date + whole days.
Containers per year = 365.25 ÷ days, rounded up.
Cost per day = price ÷ days; per year = cost per day × 365.25.

The principle

Consumption is a simple rate: amount per use times uses per day. Dividing the container size by that daily amount gives its life in days. Turning the price into a cost per day makes products of different sizes and prices comparable: a larger, dearer pack may cost less per day. Keep the size and the amount per use in the same unit, millilitres with millilitres or grams with grams.

Worked example

Default inputs: 100 g container, 1 g per use, twice a day, opened Nov 10, 2026, price $4.50.

Uses = 100 ÷ 1 = 100.
Days = 100 ÷ 2 = 50 (7.1 weeks).
Run-out = Nov 10 + 50 days = Wed, Dec 30, 2026.
Containers per year = 365.25 ÷ 50 = 7.3, rounded up to 8.
Cost per day = 4.50 ÷ 50 = $0.09; per year = $32.87.

Each point is the calculator re-run with only “Amount per use (same unit)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Amount per use (same unit)	Days it lasts
0.25	200
0.5	100
0.75	67
1	50
1.25	40
1.5	33
2	25

How to read the result

Compare cost per day between pack sizes and brands. Check the period-after-opening symbol on cosmetics (an open jar with, for example, "12M"); if it comes before the run-out date, replace the product then. Real use varies, so check the remaining amount once in a while.

Common mistakes

Guessing the amount per use; weigh or measure it a few times.
Mixing grams and millilitres for liquids of unknown density.
Forgetting other people who share the product.
Ignoring the period-after-opening date.

Keep in mind: The result is an estimate based on steady use. Follow product labels for safe use and shelf life.

Frequently asked questions

How long does a 100 g tube of toothpaste last?

At 1 g twice a day, about 50 days.

How do I compare pack sizes?

Compare the cost per day or per use, not the shelf price.

What does "12M" on a cosmetic mean?

The product should be used within 12 months after opening.

Sources: Regulation (EC) No 1223/2009 on cosmetic products, Article 19(1)(c) (period-after-opening symbol)

Checked 9 Nov 2026. Arithmetic: uses = size ÷ amount per use; days = uses ÷ uses per day; 365.25-day average year. Defaults (100 g tube, 1 g per use, twice a day) are example values.

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