How to read a supplement label.

What the panel must contain

• Serving size and servings per container.
• Each dietary ingredient, with the amount per serving.
• Percent Daily Value where one has been established. Where none exists, the row carries a dagger and the footnote “Daily Value not established”.
• The part of the plant for botanical ingredients. “Ashwagandha 300 mg” is incomplete; root and leaf are different material.
• The source compound for minerals, so the panel can be read as chemistry rather than as a name.
• Everything that is not a dietary ingredient appears below the panel, under Other ingredients.

Reading the serving line

• “Serving size: 2 capsules” means every number below it requires both capsules. A single capsule delivers half of each.
• “Servings per container: 30” on a 60-capsule bottle confirms the two-capsule serving, and tells you the bottle lasts thirty servings.
• Cost per serving, not cost per bottle, is the only honest way to compare two brands. A cheaper bottle with a smaller serving can cost more per serving.
• A larger number on the front is sometimes just a larger serving. Comparing front-of-bottle numbers between brands without checking both serving sizes compares nothing.

The limits of the percentage

• %DV is measured against a single population reference intake. It is not adjusted for age, sex, pregnancy, body size, diet, or medical history.
• Values above 100% are legal and common. A high percentage is not automatically a problem and not automatically a benefit.
• Many ingredients have no established Daily Value at all: most botanicals, most amino acids, CoQ10, probiotics. Those rows carry a dagger and cannot show a percentage, which is a gap in the reference system rather than a statement about the ingredient.
• The panel does not show the Tolerable Upper Intake Level. That is a separate published reference value, and a %DV well over 100 tells you nothing about where the upper level sits.

What any given percentage means for a particular person is a clinical question. This page describes what the number is, not what to do about it.

Why the two numbers differ

Magnesium oxide is magnesium bonded to oxygen. Magnesium contributes 24.3 of the compound’s 40.3 atomic mass units, so about 60% of the compound’s weight is magnesium and the rest is oxygen. Magnesium citrate binds magnesium to a much heavier organic acid, so the same gram of compound carries far less magnesium.

US labelling requires minerals to be declared in the Supplement Facts panel as the elemental amount, with the source compound named. Front-of-bottle copy is not bound by that rule, which is how “Magnesium 400 mg” and “Magnesium oxide 400 mg” end up on packaging that looks equivalent and is not.

Elemental fraction by mass

These are stoichiometric fractions calculated from molar masses. They describe what is in the compound, not how much of it is absorbed, which is a separate question covered in the forms guide. Hydration state shifts the number, which is why a careful label names the exact salt and its water of crystallisation.

How the rule works

• A blend declares the total weight of the blend and lists its ingredients in descending order by weight. Per-ingredient amounts are not required.
• Descending order is the only quantitative information available. It tells you a rank, not a ratio.
• A 1,500 mg blend listing eight ingredients can be 1,400 mg of the cheapest one and a dusting of the seven the marketing is about.
• Where a blend is present, cross-brand comparison for those ingredients is impossible, and no amount of careful reading fixes it.

What appears there

• Excipients: bulking agents such as microcrystalline cellulose, flow agents such as magnesium stearate and silicon dioxide, disintegrants, and coatings.
• The capsule shell: gelatin is animal-derived; HPMC and pullulan are not. This is on the Other ingredients line, not the front.
• Allergen statements. “Contains milk, soy” describes the recipe. “Manufactured in a facility that also processes…” describes the plant. They are different statements with different implications.
• Sweeteners, sugars and sugar alcohols, which is where gummy formats differ most from capsules of the same product.

Gummies also tend to carry lower and less stable actives than capsule versions of the same product, because heat, moisture and the gelling matrix limit what survives manufacture and storage.

Structure/function versus disease claims

A structure/function claim describes an effect on normal structure or function: “supports immune function”, “helps maintain healthy bones”. These are permitted without pre-market approval, and a product carrying one must also carry the FDA disclaimer, verbatim:

“This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.”

A disease claim asserts an effect on a named disease. That is a drug claim, and a dietary supplement making one is being marketed as an unapproved drug.

Three more phrases with no regulatory definition: “clinically studied” may refer to a study of a different form, at a different amount, from a different manufacturer; “pharmaceutical grade” means nothing in supplement labelling; “doctor formulated” describes who was in the room, not what came out of it.

Worth photographing when the bottle is opened

• Lot or batch number. Certification lookups and recall notices key on it. It is usually stamped rather than printed, and it is the first thing to go illegible.
• Expiration or best-by date. Voluntary for supplements in the US. Where a date is present, the manufacturer is required to have stability data supporting it.
• Storage instructions. These matter most for probiotics, fish oil, and anything hygroscopic, where the label condition is part of the potency claim.
• Probiotic count basis. “CFU at time of manufacture” and “CFU at expiration” are very different claims about the same bottle. The second one is the one that describes what you will swallow.

Frequently asked

Other guides

• What “third-party tested” actually means
• Supplement forms and bioavailability
• Supplement timing: with food, and why
• How to choose a supplement tracker app