How to read a Supplement Facts label

The front of a supplement bottle is written to sell. The back is written to rules. Every dietary supplement sold in the US has a box called Supplement Facts, and the FDA decides what goes in it and how. Five spots in that box tell you what you’re really paying for.

1. Serving size: everything is per serving

All amounts in the box are for one serving – and one serving can be one capsule, two capsules or three gummies. A bottle that proudly shows 200 mg may need two capsules for those 200 mg.

It’s common: of the 12,743 capsule, softgel, tablet and gummy products we checked, 4,181 list a serving of two or more pieces. So a bottle of 60 capsules can be just 30 servings. “Servings Per Container” can even be left out when the pack size already says it, for example “60 capsules”.

2. Amount per serving: the number you compare

This is how much of each ingredient one serving contains – the number you need for the price per dose. For vitamins and minerals, it’s the weight of the nutrient itself, not of the compound it comes in. The FDA’s own example: list the weight of the calcium, not of the calcium carbonate.

The front of the bottle plays by different rules. There, the big number can be the whole compound:

Magnesium glycinate is only about 14% magnesium – the rest is glycine, the part it’s bound to. The full story is in our magnesium guide.

3. mcg and IU: same vitamin, two units

Vitamin D has to be listed in mcg (micrograms). IU (international units) can be added in brackets. 1 mcg is 40 IU, so 25 mcg = 1,000 IU and 125 mcg = 5,000 IU (NIH (opens in a new tab)). Vitamins A and E and folate have their own conversions – they’re all in our guide to label units.

4. % Daily Value: a reference, not a target

% Daily Value compares one serving with the Daily Value the FDA uses on labels – for example 420 mg for magnesium and 20 mcg for vitamin D (FDA (opens in a new tab)). Over 100% only means one serving has more than that amount. It says nothing about quality, and more isn’t automatically better.

Many ingredients have no Daily Value at all – creatine, EPA and DHA, herbs. They get a symbol, often †, and the note “Daily Value not established”.

5. Proprietary blend: the amounts you can’t see

A “proprietary blend” – it can also have a made-up name like “Performance Matrix” – only has to show the total weight of the blend and its ingredients in order of weight. Not how much of each one is in it. In the example above, the 300 mg could be 290 mg of chamomile or 10 mg.

Which supplements use blends most, and what that means for prices: our guide to proprietary blends.

Not on this label: fish oil

“Fish oil 1,000 mg” is the weight of the oil. The omega-3 fats EPA and DHA have their own lines – add them up. Some labels also show “total omega-3”, which can include other omega-3 fats. We compare by EPA + DHA – more in our omega-3 guide.

What the box doesn’t tell you

Whether the product really contains what the label says. The FDA doesn’t approve supplements or their labels before they’re sold (FDA (opens in a new tab)). Independent seals like “NSF Certified for Sport” mean a lab has checked that the label matches what’s inside. What each seal checks.

The cost per dose in one line

Or let us do it: pick the supplement, then add your product with the price, the servings and the amount per serving from the box.