In short
- Compare cost per serving, and cost per milligram of the ingredient you actually want.
- The cheapest bottle is not always the cheapest per useful serving.
- Check how many capsules a serving needs; it changes both convenience and cost.
- Price is only one factor: form, ingredients, warnings and brand all count.
Shopping for supplements, you will often face three bottles that look comparable and carry three different prices. The sticker prices tell you very little. A fair comparison takes a pencil and four numbers from each label. Below is a worked example using three imaginary products, so you can follow the method and then apply it to real ones. These are not products in our shop; the figures are invented to illustrate the arithmetic.
The three bottles
| Bottle A | Bottle B | Bottle C | |
|---|---|---|---|
| Price | $18.00 | $12.00 | $24.00 |
| Capsules in bottle | 120 | 60 | 90 |
| Serving size | 2 capsules | 1 capsule | 3 capsules |
| Ingredient per capsule | 250 mg | 500 mg | 300 mg |
At a glance, Bottle B is cheapest and Bottle C is the most expensive. Let us see whether that still holds when we do the sums.
Step 1: servings per bottle
Divide the capsules in the bottle by the serving size.
- Bottle A: 120 ÷ 2 = 60 servings
- Bottle B: 60 ÷ 1 = 60 servings
- Bottle C: 90 ÷ 3 = 30 servings
Already the picture changes. A and B last equally long; C lasts half as long.
Step 2: cost per serving
Divide the price by the number of servings.
- Bottle A: $18.00 ÷ 60 = $0.30
- Bottle B: $12.00 ÷ 60 = $0.20
- Bottle C: $24.00 ÷ 30 = $0.80
Bottle C is four times the price per serving of Bottle B. But a serving of C contains more ingredient, so we need one more step.
Step 3: amount per serving
Multiply the amount per capsule by the capsules per serving.
- Bottle A: 250 mg × 2 = 500 mg
- Bottle B: 500 mg × 1 = 500 mg
- Bottle C: 300 mg × 3 = 900 mg
A and B give the same amount per serving. C gives 900 mg.
Step 4: cost per gram of the ingredient
This is the fairest single number. Multiply the amount per serving by the number of servings to get the total in the bottle, then divide the price by it.
- Bottle A: 500 mg × 60 = 30,000 mg = 30 g. $18.00 ÷ 30 = $0.60 per gram
- Bottle B: 500 mg × 60 = 30,000 mg = 30 g. $12.00 ÷ 30 = $0.40 per gram
- Bottle C: 900 mg × 30 = 27,000 mg = 27 g. $24.00 ÷ 27 = about $0.89 per gram
The result
| A | B | C | |
|---|---|---|---|
| Servings per bottle | 60 | 60 | 30 |
| Cost per serving | $0.30 | $0.20 | $0.80 |
| Amount per serving | 500 mg | 500 mg | 900 mg |
| Cost per gram | $0.60 | $0.40 | $0.89 |
In this example, Bottle B wins on every measure: it gives the same amount per serving as A for a third less, and it costs less per gram than C. It is also the easiest to take, with one capsule per serving, not two or three.
What the sums do not tell you
Arithmetic is one part of the decision. Before you buy, also check:
- The form of the ingredient. Two products with the same amount can use different forms, which can contain different shares of the nutrient. See Understanding ingredient forms.
- The "other ingredients". Allergens, fillers and capsule material differ.
- Whether the amount is right for you. A bigger amount is not a better one. Check the upper limits and any advice you have received.
- The label details in our label guide: warnings, lot numbers and dates.
- The brand and any independent testing it describes.
- Whether you will actually use it. A product you take consistently is worth more than a cheaper one you abandon.
A shortcut for the shop
Each product page shows the price, and the product details give serving information from the manufacturer. Use the catalog filters to put similar products side by side: filter by category, then brand, then price range, and apply the four steps above to the two or three that remain.