Methodology

The short version

• We read the figures from the pack, the brand’s page, the ARTG or a shop listing. Each one links to where we read it.
• We do the maths: compound weight × the share of it that’s magnesium. Within 15 % of the stated figure, the label adds up.
• We price the magnesium: cost per 100 mg, from the RRP or regular shelf price. Never a sale price.
• We don’t test products. We can’t tell you what’s really inside, or what a product does.
• We tell brands first. Before an “above maths” or “below maths” mark goes live, we email the brand our working and wait seven days.

The three questions, worked through

Here’s one product, step by step, with today’s figures and price. It’s an example of the method, not a pick.

Every product page shows the same steps, with a link to each source.

How much of each compound is magnesium

Each compound has a fixed share of magnesium, set by chemistry, not by the brand.

The share is the weight of the magnesium divided by the weight of the whole compound. Chemists call it the elemental fraction. It comes from standard atomic weights. The full table is on which magnesium is which.

Some compounds come in several versions; citrate has three. If the label names the version, we use its share. If not, we use our standard share, and the product page says if another version fits better.

“Amino acid chelate” with no amino acid named has no single share. Products we list with that wording: about 12 % to 20 %. So we don’t guess, and the mark is “can’t check: compound unclear”.

When a label adds up

If the stated magnesium is within 15 % of our maths, the label adds up.

The margin is wide on purpose, to cover rounding and close versions of a compound. It isn’t wide enough to hide a different citrate or compound.

Outside the margin, the two stated figures don’t fit together under the share we used. That doesn’t say which figure is right, and it says nothing about what’s in the tablet. Why it matters to you: the product page gives both numbers. Ask the brand which one the product is made and tested to.

When a blend mostly adds up

A blend “mostly adds up” when every part we can check agrees, and those parts make at least 50 % of its magnesium.

For blends we check each compound on its own. One part often can’t be checked, usually an “amino acid chelate” with no amino acid named. Each part we can check must be within 15 %, and the parts must add up to the stated total. The % beside the mark is the share of the magnesium we checked. Under 50 % checked? Then the mark is “can’t check”, and the page shows the part that does add up.

Why it matters to you: most of the magnesium behind the cost per 100 mg rests on figures that agree. The rest rests on the stated figure alone.

When we can’t check the figures

Many products say “can’t check”. That’s common, and it isn’t a mark against them.

It happens when the source gives only the magnesium figure, or names an “amino acid chelate” without its amino acid.

Why it matters to you: cost per 100 mg still works, because it uses the stated magnesium. You only lose the cross-check.

Where the figures come from

Every figure links to the page we read it from, with the date.

A figure goes in only if its page was opened during a logged check; the logs are on the updates page. We use the first of these we could open:

1. the pack itself, from a photo of the panel;
2. the brand’s own product page;
3. the ARTG public summary, the product’s page on the national register of medicines;
4. a shop’s listing.

The product page names the source, such as “the Chemist Warehouse listing”. “Label says” in the list is shorthand for whichever source we read.

The source changes the mark. Figures from a pack, brand page or the ARTG that don’t agree get “stated mg above maths” or “below maths”. A shop listing whose figures don’t agree gets the plainer “listing figures don’t match”, because listings are typed by hand. Why it matters to you: a mismatch on a listing is a reason to look at the pack, not a finding about the product.

Before a new “above maths” or “below maths” mark goes live, we email the brand our working and wait seven days. Until then the product shows a grey “under review” mark and both figures, but not whether they agree. See corrections.

What AUST L means

An AUST L number means the product is on the register. It doesn’t mean the TGA checked it.

Most magnesium supplements sold in Australia are listed medicines on the Australian Register of Therapeutic Goods (ARTG). They carry an “AUST L” number on the pack. A listed medicine may contain only ingredients from a pre-approved, low-risk list. It may make only claims from a pre-approved list of low-level uses. The sponsor, the company behind it, certifies that it meets those rules. Certifying falsely is an offence.

The TGA, the national regulator, doesn’t evaluate each listed medicine before it goes on sale. Nor does it test it against its label as a condition of listing. It can pick listed medicines for review afterwards and ask the sponsor for evidence.

Why it matters to you: AUST L tells you the product is on the register and has accepted its rules. It doesn’t tell you the TGA checked what’s in the bottle, or that it works. That’s why we show the source’s own figures and the maths.

“AUST R” marks a registered medicine, which the TGA has assessed. Few magnesium supplements are registered. Products sold under food rules, such as some sports supplements, aren’t medicines, so no AUST number applies.

If the page we read shows no AUST L number, the product page says so. That doesn’t mean the product is unlisted: listings often leave the number out. The number on your pack is the quickest way to find its register entry.

What “third-party tested” means here

We mark a product “test document linked” only when we opened the document ourselves.

Many packs say “third-party tested” or carry a program logo. That isn’t enough on its own. We need a certificate, a batch result, or the product’s listing on a testing program’s site, such as HASTA or Informed Sport.

Even a linked document shows only that testing took place, not that your batch was tested. “Testing claimed, no document found” means we found no document to open. That’s about our search, not the brand: many brands test without publishing results. “No testing claim found” is true of most products here, and isn’t a mark against them.

Prices

We use the recommended retail price (RRP), or the regular shelf price if there’s no RRP. Never a sale price.

• RRP: used only where the page prints a figure it calls the RRP, such as “RRP $32.50” or “Don’t Pay RRP $50.49”.
• Regular price: where there’s no RRP, the shelf price with no sale, promo or member marker. A shop’s everyday price, such as Chemist Warehouse’s “EDLP”, counts.

We never use sale, promotional, member, multi-buy or half-price prices. We never add a saving such as “$10.50 off RRP” back on to make an RRP. If a page shows only a sale price, we record nothing from it. Prices seen up to 27 Oct 2026 didn’t record their type. They stay on product pages as greyed history, and no figure uses them.

The headline price is the lowest current RRP or regular price we’ve seen, at any shop. No price yet? Then the product has no cost figure and sorts last. A price older than 35 days says “may have changed”. Cost per 100 mg uses the stated magnesium, because that’s the figure you’re given.

Why it matters to you: an RRP changes far less than a sale price, so products compare on the same footing. You may well pay less, so check the shop before you buy.

What the method can’t catch

• A different compound from the one stated. If both figures were written for glycinate, the maths agrees, whatever is in the tablet. Only a lab test can tell. The US service ConsumerLab found two such cases in its own testing (ConsumerLab (opens in a new tab)). We don’t test, so we can’t.
• Listings that differ from the pack. A listing can lag behind a new pack, or contain a typo.
• Changes since the date shown. Formulas, pack sizes and prices change.
• The whole market. We list 15 products, a few at a time.
• What a product does. We don’t judge effects, absorption or who it suits.

What we don’t do

• We don’t name a top pick, or a compound, dose or brand to choose. The only order we give is by a figure, such as cost per 100 mg in one form. That’s maths, not a quality rating. How to choose shows how to use it.
• We don’t say why figures differ. We say whether they agree and show the working.
• We don’t give medical advice. Whether to take magnesium, which form and how much are questions for a pharmacist or doctor.
• We take no payment from brands or retailers for listing, placement or marks. Whether we earn anything at all is on how we’re funded.

How checks run

Each week a check looks again at the prices of the eight products priced longest ago, and re-reads the four oldest labels. It adds up to five new products, and opens the register entry of each AUST L product it re-checks.

Checks are done with AI help, under a fixed procedure. The editor reviews each change before it goes live. If the data fails any test, the live site stays as it was.

When a published figure changes, the product gets a dated correction with the reason, also listed on the updates page. Corrections are never silent. To report an error, see corrections and right of reply.

The data: everything behind the list is in products.csv (for spreadsheets) and products.json, with the source of every figure. Free to reuse under CC BY 4.0 (opens in a new tab) with a link back.

Page text last revised 27 Oct 2026.