Begin at the top of Supplement Facts. Serving size changes the meaning of almost every number underneath it.
1. Find the serving size
A bottle containing 120 capsules does not necessarily contain 120 servings. If a labeled serving is three capsules, it contains 40 servings. Check both the serving size and the servings-per-container line before reading the nutrient amounts.
Directions and serving size are related but not identical. Directions can call for multiple servings over a day, or offer a range. Do not assume that one labeled serving always equals one day.
2. Read the amount and the unit together
Milligrams (mg), micrograms (mcg), grams (g), and International Units (IU) are not interchangeable. One milligram equals 1,000 micrograms. IU conversions depend on the nutrient; the vitamin D conversion cannot simply be used for every vitamin.
For minerals, look for the elemental amount in Supplement Facts. For a blend, a total blend weight may not reveal the amount of each ingredient. Missing individual amounts make some comparisons impossible; a larger total does not resolve that uncertainty.
3. Treat % Daily Value as a reference
The percentage Daily Value compares a serving to an FDA reference value used on labels. It is not a personalized prescription, an absorption percentage, or a score for product quality. “200% DV” does not mean twice the benefit.
Some ingredients have no established Daily Value. A symbol or note indicating that does not establish effectiveness or safety. It means that this particular reference value has not been established.
4. Check the rest of the formula
Read “Other ingredients,” allergen statements, and directions. Capsule shells, sweeteners, colors, and processing ingredients may matter for your dietary restrictions or tolerance. Look at the exact current product rather than relying on a general brand claim.
Two products can match on the main nutrient while differing in format and other ingredients. A label photograph is useful, but if it is incomplete or inconsistent with the listing, ask the manufacturer before buying.
5. Understand what a quality claim can show
Independent quality verification can help address questions about identity, contents, or contaminants, depending on the program. Check the exact product in the certifier’s current directory and understand the scope of the testing. A brand’s participation does not automatically cover every product it sells.
A quality seal does not prove that a supplement will work for a particular health goal or that it is right for you. FDA does not approve dietary supplements for safety and effectiveness before they are sold in the same way it approves drugs.
6. Check the purchase and your own context
Match the product name, amount, formula, count, expiration information, and seller. Compare one-time prices separately from subscription offers. Check the final total including delivery and taxes before deciding.
Then ask the question a label cannot answer: do I need this, and is it appropriate with my medicines and health conditions? Use our printable checklist as a shopping aid and bring unresolved questions to your own clinician or pharmacist.
Sources & checks
Source pages checked October 4, 2026. General health information comes from the sources below. Product amounts and prices, where shown, come from manufacturer listings. See our methodology and correction policy.
Noticed a changed label or a detail we should check? Send a correction. Save or share this guide for your next comparison.