Buying
Understanding supplement serving sizes
The front of the pack sells the ingredient. The back of the pack tells you how much of it you are getting. They are frequently different stories.
- Written by
- Candour editorial
- Published
- 2 August 2025
- Reading time
- 5 minutes
A supplement can contain an ingredient and still contain almost none of it. This is not usually deceptive in a legal sense — the ingredient is genuinely present — but it can make two products look equivalent on the front of the pack when they are nothing like each other.
Read the serving, not the container
The first number to find is what constitutes one serving. Two capsules? Three? A full scoop or a half? Products that require three capsules per serving will empty a 90-capsule bottle in a month, not three.
This matters most when comparing prices. A bottle at £20 for 90 capsules is £20 a month if the serving is three capsules, and £6.66 a month if the serving is one.
Compare the active amount
Once you know the serving, find the amount of the ingredient you actually care about. Some common places where this trips people up:
- Fish oil. The front says 1000mg. That is the oil. The EPA and DHA inside it might be 300mg or 700mg.
- Collagen. Servings across the market range from 2.5g to 15g. A five-times difference is not a rounding error.
- Botanical extracts. 500mg of a 10:1 extract is a very different thing from 500mg of dried powder. Look for the ratio.
- Live cultures. CFU counts are quoted at manufacture or at end of shelf life. The second is the more useful number.
When more is not better
A larger amount is not automatically preferable. Some ingredients have amounts used in research and going well beyond them adds cost without adding anything else. Biotin is the standard example: hair and nail formulas routinely contain many times the reference intake, and there is no particular reason to think the excess does more.
There are also ingredients where the total across everything you take matters. Zinc, iron, vitamin A and vitamin D all appear in multivitamins as well as targeted formulas. Add up what you are taking across all products rather than assessing each one alone, and if you are unsure, a pharmacist can check the total for you in a couple of minutes.
This is general information
Nothing in this article is medical advice, and none of it is a recommendation to take anything. If you are pregnant or breastfeeding, take prescription medication, or are managing a health condition, a pharmacist or GP is the right person to ask.