How we compare prices

PerDose answers one question: for a supplement you have already decided to buy, in the form you want, which product is cheapest per dose? We do not recommend what to take and we do not score quality.

What we normalise

Pack prices are not comparable: packs differ in size, servings differ in size, and labels quote amounts in different ways. For every product we work out the total amount of the ingredient in the pack and divide the price by it:

• servings = units in the pack × packs ÷ units per serving
• amount in the pack = servings × amount per serving
• price per standard dose = pack price ÷ amount in the pack × the standard dose
• cost per month = price per standard dose × 30

Every ranked row has a “Show the working” panel with these numbers and the exact words from the retailer’s listing that each one came from.

The standard dose is a comparison unit

Each ingredient has a fixed standard dose (for example 100 mg of magnesium) so that every product is measured on the same scale. It is not a recommendation of how much to take. You can type your own daily amount into any table to see costs for that instead.

How listings are read

Retailer listings are read by software that includes an AI language model. The model’s only job is to copy facts out of the listing — form, amount per serving, pack size, serving size — and quote the words each fact came from. It never sees a price and never calculates anything. A number without a matching quote from the listing is thrown away. All arithmetic is done by ordinary, tested code using the rules on this page.

What we estimate

Minerals are sold as compounds (magnesium bisglycinate, zinc picolinate). What matters for comparison is the amount of the mineral itself. If a label states it, we use it. If a label gives only the weight of the compound, we estimate the mineral content using the fraction below and mark the figure “estimated”. The fractions are calculated from each compound’s chemical formula and standard atomic weights. Real raw materials often contain water or added buffers, so an estimate can be higher than the true figure — a stated amount always wins.

Magnesium

Zinc

Calcium

Iron

Iodine

Chromium

Potassium

What we do not compare

Products are ranked only against others of the same form. Magnesium citrate is never ranked against magnesium bisglycinate, creatine monohydrate never against creatine HCl, MK-7 never against MK-4. Products with several active ingredients are kept out of the main tables, because their price cannot fairly be assigned to one ingredient. Delivery charges are not included, because they depend on the size of your basket; each retailer’s delivery terms are listed below.

What “unverified” means

If a listing does not let us confirm the amount per serving, what that amount refers to, the pack size or the form, we do not guess. The product is listed separately with the reason and is never ranked. A common example: “Magnesium Citrate 200mg” could mean 200 mg of magnesium or 200 mg of magnesium citrate — a six-fold difference.

Testing claims and dietary labels

Badges such as “testing claimed on label” or “claimed: vegan” repeat what the retailer’s listing says. We have not verified them.

Prices and updates

Prices were last checked on 17 September 2026. Each table and product page shows the date its prices were checked. The price shown is the retailer’s selling price on that date, including any sitewide promotion running at the time; voucher codes are not applied. Always confirm the price on the retailer’s site.

No paid placement

We may earn a commission when you buy through our links. It never affects the order of a table: ranking is purely price per dose, and no retailer or brand can pay for position. See the affiliate disclosure.

Report an error

Labels change and we make mistakes.Every product has a “tell us” link, or email hello@perdose.co.uk.