What does a % Daily Value over 100% mean?

That a serving contains more than the US daily value. That isn’t always bad: B12, for example, is only partly absorbed. But for vitamin D, zinc, B6, vitamin A and iron, check the dose against the UK and EU upper limits.

How is % Daily Value different from % NRV?

% Daily Value is the US measure. % NRV (nutrient reference value) is the one used on UK and EU labels. The reference amounts differ slightly, so the percentages for the same amount of a nutrient may not match.

How do I convert IU to mcg?

It depends on the vitamin. For vitamin D, 1 mcg equals 40 IU, so 1,000 IU is 25 mcg. Vitamins A and E use different factors, which our IU to mcg converter covers.

What is a proprietary blend?

A line labelled “Proprietary Blend” with the total weight of a mix but not the amount of each ingredient. It protects the brand’s formula, but you can’t tell how much of each active ingredient you’re getting. For single-purpose supplements, choose products with fully disclosed amounts.

How to Read a Supplement Label: Supplement Facts Explained

How the Supplement Facts panel is laid out

Every supplement sold in the US must carry a Supplement Facts panel. At the top are the serving size and the number of servings. Below is a list of ingredients with the amount per serving and the percentage of the daily value. Other ingredients follow in small print underneath.

A box from a high-street chemist in the UK looks different. It shows a table of nutrients per daily dose with % NRV (nutrient reference value). The logic is the same: find the amount of active ingredient in one dose. Tap a line on the interactive label to see what it means.

Two hands turn a bottle to its back label, where the serving size line and the active ingredient line are highlighted — The serving size and the amount of active ingredient matter most

Interactive label: tap a line

A sample Supplement Facts panel for magnesium. Each line explains what to look for

Supplement Facts

What it means

Serving size

Every number below is for 2 capsules, not one. This is the most common trap: "400 mg" on the front may be a 2–4 capsule dose.

Serving Size: the most important line

Serving Size is how many capsules, tablets or grams of powder make up one serving. Every number in the panel refers to that serving, not to a single capsule.

A typical case: the front of the bottle says “Magnesium 400 mg” in large print, but the panel says “Serving Size: 4 capsules”. So each capsule contains 100 mg of magnesium, and a 120-capsule bottle lasts 30 servings, not 120.

Amount Per Serving and the form in brackets

The amount is given for the elemental nutrient, and the form follows “as” in brackets:

Magnesium (as magnesium bisglycinate chelate) – 200 mg

That’s 200 mg of magnesium itself. A product called “Magnesium Glycinate 1000 mg”, on the other hand, may show the weight of the whole compound, of which only about 14% is magnesium. More on forms in our guides to magnesium and zinc.

Units

The table lists the units you’ll see most often on American labels.

Unit	Meaning	Used for
mg	milligram (1/1,000 g)	minerals, vitamin C
mcg (µg)	microgram (1/1,000 mg)	vitamins D, B12, folate, biotin
IU	international unit	vitamins D, E, sometimes A
mcg DFE	dietary folate equivalents	folate; 1 mcg folic acid with food ≈ 1.7 mcg DFE
mg NE	niacin equivalents	niacin (B3)
mcg RAE	retinol activity equivalents	vitamin A

For vitamin D, 1 mcg = 40 IU. So “125 mcg (5,000 IU)” is 5,000 IU, above the 100 mcg (4,000 IU) daily maximum set by the NHS and EFSA. For other vitamins, use our IU to mcg converter; doses of D3 are covered in our vitamin D3 guide.

% Daily Value and % NRV

% DV is the share of the US daily value. An asterisk () means no daily value has been set for that nutrient. UK and EU labels use % NRV* instead.

A figure above 100% isn’t dangerous by itself. For nutrients with low upper limits, though, check the dose against safe limits:

Vitamin D: no more than 100 mcg (4,000 IU) a day, NHS and EFSA.
Zinc: up to 25 mg a day from food and supplements, EFSA.
Vitamin B6: no more than 10 mg a day from supplements, NHS.
Vitamin A, iron and selenium: check the guide for each nutrient.

What a proprietary blend means

A Proprietary Blend line shows the total weight of a mix without the amount of each ingredient. For example, “Sleep Blend 500 mg: L-theanine, valerian, chamomile, lemon balm”. It could hold 400 mg of theanine or 10 mg, and the label won’t tell you which. When the dose matters to you, pick a product that lists every ingredient separately.

Other ingredients: what else is inside

Below the panel you’ll find the other ingredients: the capsule shell (gelatine or plant cellulose), fillers, colours and sweeteners. Look here for allergens (soy, fish, shellfish, gluten) and labels such as “vegan” or “non-GMO”. Small amounts of magnesium stearate and silicon dioxide are normal manufacturing aids and nothing to worry about.

Independent testing seals

The manufacturer fills in the Supplement Facts panel itself. Independent certification checks that what’s in the bottle matches the label:

USP Verified checks identity, purity and dissolution;
NSF Certified checks contents, and NSF Certified for Sport also screens for banned substances;
IFOS covers omega-3: EPA/DHA content, oxidation and contaminants;
Informed Sport and Informed Choice test for banned substances.

Three rosette seals with ribbons beside a laboratory flask: independent testing of what is in a supplement — A seal from an independent lab confirms the bottle holds what the label says

A product without a seal isn’t necessarily bad. A seal is simply one more assurance beyond the brand’s own word.

How to work out cost per dose

Decide the dose you need (for example, 200 mg of magnesium a day).
Use the panel to see how many capsules give that dose.
Divide the capsules in the bottle by that number to get the number of days.
Divide the bottle price by the number of days: that’s the cost per day.

Example: a 120-capsule bottle costs £18, and 2 capsules give 200 mg of magnesium. That’s 60 days, or £0.30 a day. A 180-capsule bottle costs £20, but you need 4 capsules for 200 mg. That’s 45 days, or £0.44 a day. The bigger bottle looks like the better deal, yet the first one is cheaper.

Put the numbers from your own bottle into the widget: price, capsule count and how many capsules give your dose. To compare several products side by side, use our cost-per-day calculator.

What one day's dose costs

Numbers from the bottle: price, capsule count and how many capsules give your dose

Bottle price, £ Capsules in the bottle Capsules a day for your dose

0.30 £ a day

Cost of one day's dose

The bottle lasts 60 days, about £9.00 a month

Compare on iHerb

The example on this page: £18 for 120 capsules at 2 a day is £0.30 a day; £20 for 180 capsules at 4 a day is £0.44.

A coin cut like a pie into daily slices: one slice sits on a saucer beside the two capsules for that day — Compare the cost per day, not the price per bottle

Expiry and storage

iHerb usually shows the expiry date on the product page. Omega-3, probiotics and liquid vitamins don’t like heat or light, so keep bottles closed and away from the radiator. Buy only what you’ll use before the date.

Once the label checks out, follow our step-by-step guide to ordering from iHerb.

How to read a supplement label: the Supplement Facts panel explained