Prices and value: frequently asked questions
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What does "price per dose" mean on PerDose?
Price per dose is the cost of one standard comparison amount of the actual active ingredient, rather than the price printed on the tub.
For magnesium, that might be 100 mg of elemental magnesium; for vitamin D3, 1,000 IU. We work it out from the pack price, the pack size and the amount per serving, which lets you compare a 60-capsule tub against a 360-capsule tub, or a cheap-looking product with a small dose against a pricier one with a larger dose, on the same footing. The standard amount is a comparison unit, not a recommended dose; the “your daily dose” box lets you see the same comparison at the amount you actually take.
See the full price maths explained.
Why is the cheapest pack not always the cheapest per dose?
Because the pack price alone does not say how much active ingredient you get for it.
A cheaper tub can have a smaller pack size, a smaller serving, or a lower amount per serving, so it can still work out more expensive per dose than a pricier tub with more in it. A £7 tub of 30 capsules at 100 mg each and a £12 tub of 180 capsules at 100 mg each look very different by price, but the second is cheaper per dose once you divide by how much active ingredient the whole pack contains. Sorting our tables by price per dose (the default), rather than by pack price, is what surfaces this.
Sort any table by price per dose or per pack price.
How do I calculate cost per milligram myself?
Divide the pack price by the total amount of active ingredient in the whole pack, then multiply by the amount you want the cost for.
“Total amount in the pack” is the servings in the pack multiplied by the amount per serving; multiplying by, say, 100 gives you the cost per 100 mg. As a worked example: a £14.99 tub of 180 capsules, two per serving, providing 200 mg of magnesium per serving, gives 90 servings and 18,000 mg of magnesium in the whole pack — £14.99 ÷ 18,000 mg is about 0.083p per mg, so about 8p per 100 mg. We run this same calculation for every product, using the elemental or active amount rather than the compound’s raw weight where the two differ.
See the full worked example with real numbers.
How do I work out how long a tub will last?
Divide the pack’s total servings by how many servings you take a day.
This gives you the number of days the pack will last, which we show as “days’ supply” on every product’s expanded row. For example, a pack with 90 servings, taken one serving a day, lasts 90 days; the same pack taken twice a day lasts 45 days. This is different from the number printed on the tub as “servings”, which assumes the label’s own suggested serving size rather than the amount you actually take — use the “your daily dose” box to see days’ supply recalculated for your own amount.
Why do prices differ so much between retailers for the same product?
Retailers set their own prices, and their margins, promotions, stock levels and how recently they discounted or restocked all vary independently of each other.
This means the same tub from the same manufacturer can genuinely cost noticeably different amounts at different retailers on the same day. Some retailers also run permanent site-wide discount codes that make their list price look higher than what most shoppers actually pay; we compare list prices as shown in each retailer’s feed, since we do not yet track discount-code-adjusted prices. Checking a few retailers in our table for the exact product you want, rather than assuming the cheapest-looking one is always cheapest, is worth doing for anything close.
Compare retailers for any product across our tables.
Are own-brand supplements cheaper per dose?
Not consistently, on our current data.
Own-brand products (a retailer’s own-label range) sit close to the middle of the price range within their class, rather than reliably undercutting other brands. Looking across our currently ranked products, own-brand offers land almost exactly at the typical (median) price per dose for their class, while non-own-brand offers are only marginally cheaper on the same measure — not a large or consistent gap either way, and the picture can shift as feeds and prices change daily. This is a factual read of the current tables, not a recommendation to buy one over the other.
Compare own-brand and other brands directly in any table.
Do bigger packs always cost less per dose?
No — it is a common pattern, but not a rule.
Manufacturers often price larger packs lower per dose to encourage a bigger purchase, but this is not guaranteed, and some large “value” packs are priced no better, or even worse, per dose than a smaller pack of the same product. This is exactly why we highlight “best value under six months’ supply” alongside the outright cheapest per dose: the cheapest pack per dose is sometimes a two-year supply, which is not always the practical choice, and checking both figures rather than assuming bigger is automatically cheaper avoids overpaying for either.
See pack sizes compared by price per dose in any table.
Do gummies cost more per dose than tablets?
Yes, generally: on our current data, gummy products work out noticeably more expensive per dose than tablets or capsules of the same ingredient.
This reflects the more involved manufacturing process and smaller typical active amount gummies tend to carry per piece. It is a small, current sample rather than a fixed rule for every ingredient, and it can shift as more gummy products are added to our feeds. It is a factual pattern in the pricing, not a judgement of gummies as a form — some people prefer them for other reasons than price, such as not needing to swallow a capsule.
Compare gummies against tablets and capsules for any ingredient.
What is the difference between "estimated" and "stated"?
“Stated” means the figure came directly from the label; “estimated” means we calculated it from a conversion factor.
“Stated” covers a printed elemental or active amount, or an exact compound weight we used as given. “Estimated” applies where the label only gave the compound’s weight, so we applied a published conversion factor to work out the elemental or active amount — always marked “≈” and “(estimated)” so it is never shown as if it were as certain as a stated figure. We only estimate where an established, sourced factor exists for that exact form; where a label is ambiguous and no reliable factor applies, the product is marked unverified instead.
See the conversion factors we use and their sources.
What does "unverified" mean, and why is a product missing?
“Unverified” means a listing did not give us enough information to work out a reliable price per dose for it.
This can be an unclear amount per serving, an unstated pack size, or an ambiguous form. Rather than guess at a missing figure, we leave the product off the site until its label has been read and confirmed from the retailer’s own page text (for example, an ambiguous magnesium amount with no cue as to whether it means the compound or the elemental figure). An unverified product may well be a perfectly good product — it simply means the listing text did not yet let us compare it fairly against the others.
See what is left out and what triggers it.
Why do you rank on the label's amount by default, and what does the "active content" switch do?
We rank on the label’s own printed weight by default because that is what most people are actually looking at when they choose between packs.
This holds even for products where that weight has to be converted to give the active content, such as citrulline malate providing L-citrulline, or choline bitartrate providing choline. The “Compare by active content, not label weight” checkbox switches every figure in the table to the converted active amount and re-ranks by that instead. It only appears on tables that actually contain a converted product — everywhere else, the label’s weight already is the active content. Both figures are always calculated in advance; neither is worked out in your browser.
Try the active content switch on a table that has one.
How does the "your daily dose" box change the numbers?
It is a single number field, pre-filled with our standard comparison dose, that recalculates every row’s numbers the moment you change it.
Price per dose, cost per month, and days’ supply all update for every row in the table, using the same numbers behind the standard comparison; nothing is sent anywhere, and the maths runs in your browser. This lets you see real costs at the amount you actually take, rather than the round comparison figure we use to keep every product on the same footing. The number you enter is kept in the page’s web address, so you can share or bookmark the table already set to your own dose.
Try changing your dose on any comparison table.
Do you include delivery costs? Subscription prices? Discount codes?
No to all three: we rank on each retailer’s list price only.
Delivery cost is not folded into the ranking, because it depends on the rest of your basket and whether you clear a retailer’s free-delivery threshold, which we cannot know from a single product; we show the retailer’s shipping rule separately instead. Subscribe-and-save pricing and one-off discount codes are not captured either, since they depend on a scheme or a code that is not part of the plain listing price, and can change or expire independently of the price we read from the feed. Always check the retailer’s own checkout for the final price, including delivery or any active offer.
See each retailer’s shipping rule noted on our tables.
How often are prices updated, and at what time?
Prices refresh automatically once a day, starting at 06:23 UK time (05:23 in winter).
That refresh pulls the latest data from each retailer’s product feed and rebuilds every table; the exact time a specific page finishes updating can be a few minutes after that, once the full pipeline has run. Every table shows “Prices last checked” with the date of its most recent refresh, so you can always see how current the figures you are looking at are. Because this is a daily batch process rather than a live feed, a price that changed on a retailer’s own site within the last day may not yet be reflected here.
Check the “Prices last checked” date on any table.
Why is a product I bought not listed?
Either the retailer is not yet one of our feeds, the product has since gone out of stock or been delisted, or its listing did not clearly match one of the ingredients we compare.
A retailer that is not one of the feeds we read simply will not appear yet; a product that went out of stock or was delisted since our last refresh will drop out too; and a listing whose title and description did not clearly name one of our compared ingredients would not be picked up automatically. We are steadily adding more retailers and ingredients, but coverage is not yet complete for every UK seller or every supplement. The quickest way to flag a missing product is the report link on the relevant page.
Why does Amazon show no price on PerDose?
Amazon only lets its prices appear on other sites through its own product data service, for at most 24 hours after the price was fetched.
So a product only shows an Amazon price when that data is currently available to us, refreshed daily, not permanently on or off. Until, or between, that data being available, every matched product instead carries a “View this product” link straight to the same item on Amazon (matched by hand from its barcode or label), or a barcode search where no exact match has been made yet — deliberately without a price, so nothing shown could be out of date. When Amazon pricing is available, it appears as an ordinary ranked row like any other retailer, marked with the time it was fetched.
Read the full Amazon section of our disclosure.
Does PerDose earn money when I click? Do retailers pay to be listed or ranked?
We earn a small commission when you buy something after following one of our links, at no extra cost to you; this is how the site supports itself.
No retailer or brand pays to be listed, to be ranked higher, or to have their products featured — every table is ordered purely by price per dose, calculated the same way for every product regardless of who sells it. A retailer that pays no commission at all is ranked exactly the same way as one that does, using the same formula. If we ever changed this, we would say so clearly rather than let it go unstated.
Read the full affiliate disclosure.
What does "best value under six months' supply" mean?
It highlights the cheapest per-dose product whose pack does not last longer than roughly six months at the standard comparison dose.
This is shown as a second highlight alongside the outright cheapest per dose, because the absolute cheapest price per dose is sometimes a pack so large it takes years to use. A two-year tub can look unbeatable on pure price per dose, but committing that much money and cupboard space to one product is not always the practical choice, especially for something you are trying for the first time. This second highlight is computed from the pack’s own days’ supply figure, using the same numbers as every other row.
See this highlight on any comparison table.
Why are combination products shown separately?
A combination product carries more than one active ingredient beyond the accepted cofactors for its main ingredient, so its price covers several ingredients at once.
Examples include a full multivitamin, or a magnesium-and-zinc product, as opposed to accepted pairings such as magnesium with vitamin B6, or D3 with K2. Ranking a combination product directly alongside single-ingredient products would understate what you are actually paying for, since part of the price is for the other actives too. Combination products are shown in their own section with a badge naming what else they contain, and the price per dose shown counts only the ingredient whose table you are viewing.
See combination products in their own section.
What is the difference between "per month" and "per dose"?
“Per dose” is the cost of one standard comparison amount; “per month” is that same figure multiplied by 30.
“Per dose” is the fairer figure for comparing two different products or pack sizes directly; “per month” puts the same underlying price in a scale that is easier to picture for a habit you might keep up for a while, based on taking the standard dose every day for 30 days. Both numbers describe the same underlying price, just at a different scale. Both are shown on every row, and both recalculate together if you change “your daily dose”.
See both figures together on any comparison table.