Beauty Product Comparison Tool: Compare Price and Features
Enter the price and size of two or three beauty products to compare the price for the same amount, the cost of each use, and how many of your chosen…
Product Usage & Refill Planning
Skincare Product Refill Calculator: Plan Your Next Purchase
Enter the size of a product and how often you use it to see how many days it will last, the date it runs out, the date to buy the next one, and the cost of each use.
The skincare refill calculator estimates how long a product will last at the rate you use it, and tells you when to buy the next one so that you do not run out.
What this tool does
It divides what is left in the pack by the amount you use each day. From that it works out the number of uses and days left, the date the product runs out and the latest date to buy a replacement. With a price, it also shows the cost of each use and of each month.
What you enter
| Field | What to enter | Limits |
|---|---|---|
| Product | The kind of product. Each has a typical amount per use. | Required |
| Size of the product | The net content printed on the pack | 0.1 to 5,000 |
| Unit | Milliliters, grams, fluid ounces or ounces | Milliliters if not changed |
| Amount per use | Your own amount, in ml or g | Optional, 0.01 to 500 |
| Uses per day | For example 2, or 0.5 for every other day | 0.1 to 20 |
| Already used | The share that is gone, in percent | Optional, 0 to 99 |
| Counting from | The start date | Optional. Today if left empty |
| Days needed to buy a new one | Shopping or delivery time | 0 to 90. Seven if left empty |
| Price | In any currency, without a currency sign | Optional |
Use a point for decimals, as in 1.5. A comma is read as a thousands separator.
Typical amounts per use
| Product | Amount per use |
|---|---|
| Face moisturizer, hand cream | 1 ml |
| Face cleanser, toner or essence | 1.5 ml |
| Serum | 0.4 ml |
| Face sunscreen, for face and neck | 1.25 ml |
| Eye cream | 0.25 ml |
| Body lotion, for the whole body | 25 ml |
These are round, typical figures. If you choose "Another product", you must enter your own amount.
How the result is worked out
- Fluid ounces are converted at 29.5735 ml, and ounces at 28.3495 g.
- Content left = size × (100 − percent used) ÷ 100.
- Uses left = content left ÷ amount per use, rounded down.
- Days left = content left ÷ (amount per use × uses per day), rounded down.
- Runs out = start date + days left. Buy by = that date − the days needed to buy.
- Monthly use = amount per use × uses per day × 30.44.
- Cost per use = price ÷ the number of uses in a full pack.
Messages you may see
- "Choose the kind of product." and "Enter the size of the product." when a required field is empty.
- "Uses per day must be between 0.1 and 20." when a number is outside its limits.
- "The size of the product must be a number." when a field holds letters.
- "Enter the amount you use each time for this product." when you chose "Another product" without an amount.
- "Choose a date within the last five years or the next year." for a start date outside that range.
The result also warns you when the date to buy has already passed, or when less than one use is left.
Worked example
A 50 ml face moisturizer, used twice a day, new, with no amount entered. The typical amount is 1 ml, so the pack holds 50 uses and lasts 25 days. Counting from 7 October 2026, it runs out on about 1 November 2026, and with seven days to buy, the date to buy by is 25 October 2026. You use about 60.9 ml a month.
Limits and assumptions
The estimate assumes that you use the same amount every time, and that all of the product can be got out of the pack. Sizes in grams or ounces are counted in grams. A product may need replacing before it is empty: check the period after opening on the pack, or use the Beauty Product Expiry Tracker.
Related on ArniSun
Frequently asked questions
How do I find my real amount per use?
Note the date you open a product and the date it is empty. Divide the size by the number of uses in that time. Enter the answer as your own amount for a closer estimate next time.
Why does my sunscreen last longer than the calculator says?
Most people apply less sunscreen than the amount used in testing. If a tube lasts much longer than the estimate, you may be applying too little. See [[BLOG-031]] for how much to use.
Does the calculator store my products?
No. The numbers are used to work out the result and are not kept.