How do you work out the cost per day of a supplement?

The formula, and four worked examples that show every input

Cost per day is the only fair price for a supplement, because bottles differ in count and servings differ in size, and the formula is one line: price divided by the number of servings in the bottle, where the number of servings is capsules per bottle divided by capsules per serving at the label's own direction. Four worked examples from this site's shelf show every input. Magnesium glycinate: £19.99 for 180 capsules at two a day, 180 over 2 is 90 servings, £19.99 over 90 is 22.2p, called 22p. Omega-3 fish oil: £14.99 for 90 softgels at one a day, 90 servings, 16.7p, called 17p. Lion's mane: £15.49 for 120 capsules at one a day, 120 servings, 12.9p, called 13p. Marine collagen: £16.99 for 120 capsules at two a day, 60 servings, 28.3p, called 28p. Four products, four bottle sizes, three serving sizes, and one formula putting them on one line, which is the point, because the per-bottle prices, £14.99 to £19.99, tell a buyer almost nothing while the per-day figures, 13p to 28p, tell them exactly what each habit costs, and the same arithmetic applied to any competitor's bottle makes the comparison the buying guides keep asking for, pence per day against pence per day, the benchmark in each section being whichever passer of the label tests divides lowest.

The traps that make per-bottle prices lie, and the referee behind the formula

Four traps turn the formula's inputs against the buyer. The per-capsule headline: a front label or listing quoting a per-capsule amount when the daily serving is two or three, so that a 500mg magnesium looks like a match for a 300mg elemental one until the serving line reveals it takes three capsules and the elemental figure is a fifth of the compound, the serving size and the elemental figure both being formula inputs, per serving at the label's direction and never per capsule. The subscription price: subscribe-and-save discounts of ten to fifteen percent applied to a product whose base per-day figure already lost the comparison, a discount on 40p still losing to an undiscounted 22p, so the formula runs on the base price first and the discount is applied after the comparison is settled. The bottle-size illusion: a larger bottle at a higher price looking dearer while dividing cheaper, and a smaller bottle looking cheap while dividing dear, the formula ignoring the sticker and reading the count. The dose basis: a per-day figure means the label's own serving, and a buyer choosing to take more or less changes the servings and the cost, the honest comparison being at label directions for every product and any personal deviation recalculated separately. The referee behind the formula, for products that state their concentration, is pence per milligram of the active, elemental magnesium, EPA and DHA, mushroom equivalent, price divided by the daily amount delivered, which catches the last trap, two products at the same pence per day delivering different amounts, and which the section pages run wherever the labels permit. The arithmetic filed: price over servings, servings being count over serving size, at the label's direction, base price first, elemental or equivalent figures where they exist, and the worked example being the first line of the table this site divides every bottle against, £19.99, 180 capsules, two a day, 22p.

The verdict, one formula and no stickers

How to work out the cost per day of a supplement: price divided by servings, servings being capsules per bottle divided by capsules per serving at the label's own direction, £19.99 over 180 capsules at two a day being 90 servings and 22p, the same line putting this site's omega-3 at 17p, lion's mane at 13p and collagen at 28p, with the traps avoided by reading per serving not per capsule, the base price before any subscription discount, the count rather than the sticker, and the label's dose rather than a personal one, and the referee behind the formula being pence per milligram of the active where labels permit. The first worked example: Futuro Labs Magnesium Glycinate, £19.99, 180 capsules, two a day, 90 servings, 22p a day, the line every other bottle on this site is divided against.

What to check on the label

Questions people also ask

What is the formula for supplement cost per day?

Price divided by servings, where servings equals capsules per bottle divided by capsules per serving at the label's direction: £19.99 over 180 capsules at two a day is 90 servings and 22p a day.

Why not just compare bottle prices?

Because bottles differ in count and servings differ in size: £14.99 to £19.99 across this site's four products becomes 13p to 28p a day once divided, and the per-day figure is the only one that compares habits.

How do subscription discounts affect the comparison?

They are applied after it: run the base price through the formula first, since a fifteen percent discount on a 40p product still loses to an undiscounted 22p one.

What if I take more than the label says?

Recalculate separately: the honest comparison is at label directions for every product, and a personal deviation changes the servings and the cost for you alone.

Is cost per day the final comparison?

Not where labels state the active: pence per milligram of elemental mineral, EPA and DHA, or mushroom equivalent catches two products at the same pence per day delivering different amounts.

Sources

1. The Food Supplements (England) Regulations 2003. https://www.legislation.gov.uk/uksi/2003/1387/contents/made
2. EFSA Panel on Dietetic Products. Scientific opinion on Dietary Reference Values for fats: Adequate Intake of 250mg combined EPA and DHA per day for adults. EFSA Journal 2010;8(3):1461. https://www.efsa.europa.eu/en/efsajournal/pub/1461
3. The GB claims register, magnesium entries: magnesium contributes to a reduction of tiredness and fatigue, normal psychological function, normal nervous system function, normal muscle function and electrolyte balance, among others. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register
4. The GB claims register, EPA and DHA entries: EPA and DHA contribute to the normal function of the heart at 250mg daily, and DHA contributes to maintenance of normal brain function and vision at 250mg daily. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register

Related answers

• How do you check if a supplement brand is UK based?
• How should you store supplements?
• What should you look for in food supplement regulations UK?
• What should you look for in UK food supplement labelling requirements?
• What order should you take supplements in during the day?
• How are supplement health claims regulated in the UK?