Do third-party tested supplements cost more?
Usually, yes. In 12 of the 15 categories where a certifier names at least one package we can price, the cheapest certified product costs more than the cheapest product overall: 1.1× to 17× as much per dose. In 3, the cheapest product is itself the cheapest certified one. In 8 more, nothing we track is certified at its package, so there is no certified price to compare.
Certified here means a certifier's own scope covers the exact package sold: NSF names package sizes on each listing, and USP names the product and puts its mark on the label, so a USP row counts when both are true. Across all 385 products we track, 87 clear that bar. It says an outside program tested that product for what the program tests for. It does not mean a cheaper product is unsafe, and neither column says anything about whether a supplement will work for you. Both columns are shelf prices per comparison dose before delivery, measured the same way, so a category page's pick, which also needs a published delivery rate, can be a different product. The second figure in each cell is that price over thirty comparison doses, one a day, which is a way to read the first figure and not a suggestion of how much to take.
3 vitamin D products sit outside the strength bands this site ranks (below 400 IU or above 10,000 IU per serving) and are left out of the vitamin D rows. Products above 10,000 IU are sold as weekly or monthly doses, so the site never gives them a cheapest claim.
Each category's own “which brands are third party tested” page splits the rest into listed at another size, searched and not found, and not settled either way.
Related: the cheapest NSF certified creatine, per 5 g, and is Thorne creatine worth the price?
Every category we compare: the home page. Every question we answer: the question index.
What this rests on: prices we last recorded at the retailer named on each product page, which go stale, and each page says when it was checked; the products we track, not every product sold, and Amazon and Walmart are not among the stores; listings and labels read at the source, each linked from the page. Found an error? Tell us. The full method: How we compare.