A supplement cost per serving comparison comes down to one division: price divided by servings per container, not by the capsule count. A $19 supply holding 90 servings costs $0.21 each. A cheaper looking $16 supply with 45 servings costs $0.36. The lower number on the tag is 70% more expensive at the point you actually swallow it.
The serving line is the one people skip
Serving size sits under the supplement facts panel in small type, and it is the single most useful figure on the label. One product defines a serving as one capsule and another defines it as two, so two containers with identical capsule counts can differ by a factor of two in how long they last.
This is where a bigger container can quietly lose. A 180 count sounds like three times the value of a 60 count, until you read that its serving is three capsules, which makes it 60 servings. Same supply, more packaging, higher cost.
A cost per serving comparison, worked through
| Measure | Option A | Option B |
|---|---|---|
| Price | $16 | $19 |
| Capsules | 90 | 90 |
| Serving size | 2 capsules | 1 capsule |
| Servings per container | 45 | 90 |
| Cost per serving | $0.36 | $0.21 |
Same capsule count. Same shelf. A $3 difference that runs the wrong way once you divide. Anyone comparing these two by the headline figure picks the worse one every time, and that is the trap a cost per serving comparison exists to close.
This same trick shows up in bundles, where two products are priced as a set and the set figure looks like a discount. Price the set per serving before you accept that framing. Sometimes it's a genuine saving on two products you'd have bought anyway. Sometimes it's two supplies with generous serving sizes sold at a figure that only beats one of them.
Then check what the serving delivers
Cost per serving only compares fairly if the servings do comparable work. If option B's single capsule carries 200 mg of elemental magnesium and option A's two capsule serving carries 400 mg, A is delivering twice as much per dose and the per serving figures aren't the same currency.
Divide again, this time by the dose. Cost per 100 mg is the figure that survives across different concentrations, and it's how you weigh a 200 mg capsule at $0.21 against a 400 mg serving at $0.36. The second is better value despite the higher serving cost.
Quality narrows the field before price sorts it
Cheap forms exist for a reason. Magnesium oxide carries more elemental magnesium per gram than magnesium glycinate and costs a fraction as much, and it also draws water into the gut in a way that some people notice within a day. Price alone will steer you toward forms that don't suit you.
So sort first, then compare. Shortlist products whose form and dose you're actually willing to take daily, put them in a table like the one above, and let cost per serving break the tie. That order prevents the most common mistake, which is optimising the cost of the wrong capsule.
Form matters because it changes the arithmetic underneath. Two magnesium products can carry the same 200 mg claim on the front of the container and different amounts your body can use, since the figure on the label describes the compound rather than the mineral. Comparing them per capsule is comparing two different products that happen to share a word.
The limit of the method
Cost per serving assumes you take the full serving. Anyone who splits capsules or takes one where the label says two is running a different calculation than the one on paper, and the cheaper option may win again. Doses also aren't interchangeable across forms, so a per milligram comparison between magnesium oxide and magnesium glycinate is a shape comparison, not a like for like one.
Run the division. Price divided by servings, then by dose if the servings differ. It takes thirty seconds and it's the only figure that means the same thing across two different containers.
Keep both supplies on the same page while you do it. Comparing one in your hand against one you remember is how the wrong option wins, because memory keeps the figure and drops the serving size. Write both columns down and the answer usually stops being interesting.
Frequently asked questions
How do I compare two bottles?Show answerHide answer
Divide price by servings per container, then check what each serving actually delivers.
Why does the bigger bottle not always win?Show answerHide answer
Sometimes it has the same number of servings in more capsules, which means bigger doses rather than better value.
What about quality?Show answerHide answer
Compare tested products first, then compare cost among those.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
