This is a published example of what a few minutes of division can find.
In 2011, researchers at the Oregon State University and Oregon Health & Science University College of Pharmacy reviewed fish oil supplements listed in the National Library of Medicine’s Herbal Supplement Database. They identified 163 products, kept 102 that met their entry criteria, and then did something most shoppers never do: they calculated how many servings of each product it would take to deliver 3,360 milligrams of combined EPA and DHA, the FDA-approved dose of the prescription version, and what a month of that would cost.
The median non-liquid product took 11.2 servings a day and cost a median of $63.49 a month. The median liquid product took 3.6 teaspoons a day and cost a median of $13.60 a month. Same active ingredients, same target amount, nearly a fivefold difference in the monthly bill. Only 22 percent of the products met the authors’ combined standard, which included reaching that dose for under $50 a month in fewer than eight servings a day.
Nobody could have seen that by looking at shelf prices. You only see it after you divide.
Americans spend real money here. A National Center for Health Statistics report published in June 2016, drawing on 2012 National Health Interview Survey data, put total US out-of-pocket spending on complementary health approaches at $30.2 billion, with $12.8 billion of that going to natural product supplements. Mean spending per user on natural products was $368 a year. That’s 2012 data, and it’s the most recent figure of its kind we could verify, but it sets the scale: this is a category where getting the math wrong costs a couple hundred dollars a year without anyone noticing.
The easy half: price divided by servings
Cost per serving is the calculation most people already know, and it’s worth doing because it takes ten seconds.
Cost per serving = price ÷ servings per container
The catch is the second number. FDA’s dietary supplement labeling guide defines a serving as the maximum amount the label recommends for a single eating occasion. If the label says take two to three capsules daily, the serving is three capsules. If the label recommends nothing, one unit is the serving.
So servings per container is the count divided by the units per serving, not the count on the front of the bottle. A 180-capsule bottle with a three-capsule serving is a 60-day supply.
There’s a wrinkle here that almost nobody knows. FDA’s guide says the “Servings Per Container” statement isn’t required when it would simply repeat the net quantity of contents, which is the count on the front panel. A 100-tablet bottle at one tablet per serving doesn’t have to print “100 servings” anywhere. FDA’s chapter on net quantity also lets a manufacturer state contents by weight or measure instead of by count, so even the tablet count isn’t guaranteed.
When that line is missing, the division is yours. Count divided by units per serving. Write it down.
The half that matters: price divided by milligrams
This is the step that changes answers, and it’s the one almost nobody takes.
Cost per milligram = price ÷ (servings per container × milligrams per serving)
Multiply by 1,000 if you’d rather think in grams. Either way, you’re now measuring what you’re buying instead of how the product is packaged.
Cost per serving tells you the price of a ritual. Cost per milligram tells you the price of the substance. Those are different questions, and products are packaged in ways that keep them from lining up. One company puts 200 milligrams in a capsule and calls three capsules a serving. Another puts 900 milligrams in one capsule. Both are legal, both are clear on the label, and neither is trying to help you compare.
Two worked examples follow. The numbers are invented and deliberately round so you can check the arithmetic yourself. They are not real products or real prices.
Worked example one: two bottles of fish oil
Product a. $18 for 180 softgels. The label calls three softgels a serving and lists 600 milligrams of combined EPA and DHA per serving.
- Servings per container: 180 ÷ 3 = 60
- Cost per serving: $18 ÷ 60 = 30 cents
- Total EPA and DHA in the bottle: 60 × 600 mg = 36,000 mg, or 36 grams
- Cost per gram: $18 ÷ 36 = 50 cents
Product b. $24 for 60 softgels. The label calls one softgel a serving and lists 900 milligrams of combined EPA and DHA per serving.
- Servings per container: 60
- Cost per serving: $24 ÷ 60 = 40 cents
- Total EPA and DHA in the bottle: 60 × 900 mg = 54,000 mg, or 54 grams
- Cost per gram: $24 ÷ 54 = about 44 cents
Product A wins on cost per serving, 30 cents against 40. Product B wins on cost per gram, 44 cents against 50. The $24 bottle is the cheaper buy, and the $18 bottle is the one that looks cheaper.
Run it one more way, matched on daily amount, and the gap gets concrete. Product A delivers 200 milligrams per softgel, so 900 milligrams a day takes 4.5 softgels. At that rate the 180-count bottle lasts 40 days, which works out to about 45 cents a day. Product B delivers 900 milligrams in one softgel, so the 60-count bottle lasts 60 days at 40 cents a day.
The bottle with three times as many pills is the shorter supply. That’s the whole lesson in one sentence.
Worked example two: when the bigger number is the smaller dose
Minerals come as compounds, and only part of the compound is the mineral. This is where the front of the package can hand you the wrong answer entirely.
The NIH Office of Dietary Supplements reports that calcium carbonate is 40 percent calcium by weight and calcium citrate is 21 percent. Federal regulation handles this on the Supplement Facts panel: under 21 CFR 101.36, the listed amount must be the weight of the mineral itself rather than the weight of its source, which is why panels read “Calcium (as calcium carbonate).” The front of the box follows different rules, and that’s where the compound weight shows up in big type.
Product c. Front of the bottle: “Calcium Carbonate 1,250 mg.” $8 for 100 tablets, one tablet per serving.
- Calcium delivered: 1,250 mg × 40% = 500 mg per serving
- Servings per container: 100
- Cost per serving: $8 ÷ 100 = 8 cents
- Total calcium in the bottle: 100 × 500 mg = 50,000 mg, or 50 grams
- Cost per gram of calcium: $8 ÷ 50 = 16 cents
Product d. Front of the bottle: “Calcium Citrate 1,500 mg.” $14 for 120 tablets, two tablets per serving.
- Calcium delivered: 1,500 mg × 21% = 315 mg per serving
- Servings per container: 120 ÷ 2 = 60
- Cost per serving: $14 ÷ 60 = about 23 cents
- Total calcium in the bottle: 60 × 315 mg = 18,900 mg, or 18.9 grams
- Cost per gram of calcium: $14 ÷ 18.9 = about 74 cents
Product D’s front number is larger, 1,500 against 1,250. Product D’s dose is smaller, 315 milligrams of calcium against 500. And per gram of calcium, Product D costs more than four times what Product C costs.
Now the honest counterweight, because cheapest per gram is not automatically the right buy. The Office of Dietary Supplements notes that carbonate dissolves less well when stomach acid is low and performs better taken with a meal, while citrate depends less on stomach acid and can be taken without food. For someone taking acid-reducing medication, the expensive form may be the one that works. ODS also reports that absorption falls as the amount taken at once rises, about 36 percent of a 300-milligram dose against 28 percent of a 1,000-milligram dose, and states plainly: “Absorption from supplements is highest with doses of 500 mg or less.”
So the arithmetic gives you a defensible number. It doesn’t give you the decision by itself.
Units that don’t convert the way you expect
Before you divide, make sure both labels speak the same language.
Vitamin D is the easy case. The Office of Dietary Supplements gives 1 microgram as 40 IU, a fixed conversion, so 25 micrograms and 1,000 IU are the same amount. Under 21 CFR 101.36, supplement panels must declare vitamin D in micrograms, with any IU figure in parentheses afterward.
Vitamin E is the hard case, and it catches people who think an IU is an IU. The Office of Dietary Supplements gives 1 IU as 0.67 milligrams of the natural form, d-alpha-tocopherol, but only 0.45 milligrams of the synthetic form, dl-alpha-tocopherol. Weight for weight, ODS says synthetic alpha-tocopherol is about half as active. Divide two vitamin E prices by IU without checking the form and you’ll get a number that means nothing.
Our companion article on comparing similar products goes through the rest of the attribute checks, including form, standardization and verification, that should happen before any price math at all.
Where the arithmetic is impossible
Some products cannot be put through this calculation, and that’s useful information in itself.
A proprietary blend is a group of dietary ingredients disclosed together. Under FDA’s labeling rule at 21 CFR 101.36, the amount shown for the blend is “the total weight of all other dietary ingredients contained in the proprietary blend.” The ingredients inside appear underneath in descending order by weight, with no individual amounts.
So for a blended product you can calculate cost per serving, and that’s where you stop. Cost per milligram of the ingredient you came for is not computable, because the milligrams aren’t disclosed. There are legitimate formulation reasons for blends, and this isn’t an accusation. It’s a limit. When two products are otherwise similar and one of them blocks the only calculation that reveals value, that’s a reason to put it second. Our article on the Supplement Facts panel covers how blends are built and what else they hide.
Raw botanical powders create a softer version of the same wall. A 2026 paper in The Journal of Nutrition argues that a declared raw botanical powder gives you no basis for estimating active constituent content, because the form itself carries no standardization. A standardized extract usually states a percentage of a marker compound, which gives you something to divide. A plant name and a weight does not.
One more caution before you trust your own number. The milligrams you divide by are a label claim, and published analyses keep finding gaps. A 2026 study in the journal Foods measured lycopene in commercial supplements and reported marked inconsistencies between declared and measured content, with one method finding concentrations up to 70 percent above the label. Third-party verification is the partial answer here. USP’s Dietary Supplement Verification Program, a private voluntary program, evaluates enrolled products against standards for quality, purity, potency, performance and consistency, and maintains a public list of participants you can check.
The costs that aren’t on the shelf tag
The sticker price is rarely the price.
Shipping and tax. Add them before you divide, especially on a small bottle where $6 of shipping can swamp a 20 percent price difference.
Subscriptions. A subscribe-and-save discount is real money, and a subscription you forget to cancel is real money going the other direction. Run the math on the discounted price, then separately ask whether the shipping interval matches how fast you’ll use the product. Our article on wellness subscriptions covers how those schedules are built and how to audit your own recurring charges.
Bulk. A two-year supply at a lower cost per milligram is only a saving if you finish it. Check the date on the bottle. Notably, FDA’s labeling guide chapter on other labeling information covers iron warnings, folic acid and organic claims and doesn’t set an expiration-date requirement at all, so treat any date printed on a supplement as the manufacturer’s own statement rather than a federal standard.
Multi-capsule servings. Worth repeating because it’s the most common surprise: a bottle that looks like a six-month supply at one capsule a day is a two-month supply at three. The reorder cycle, and the shipping charges attached to it, triple with it.
What a low cost per milligram can’t tell you
The arithmetic has a failure mode, and it’s an important one. Cheaper per milligram usually means more milligrams per dollar, and more is not always better.
Vitamin D makes this visible. A high-dose softgel is almost always cheaper per IU than a low-dose one. But the Office of Dietary Supplements reports Tolerable Upper Intake Levels for vitamin D ranging from 25 to 100 micrograms, which is 1,000 to 4,000 IU, depending on age. ODS adds that the Food and Nutrition Board considers signs of toxicity unlikely below 250 micrograms, or 10,000 IU, a day, while noting that lower intakes may still cause harm over time. Iron behaves the same way. ODS notes that iron-only supplements often supply 65 milligrams, which is 360 percent of the Daily Value, and that intakes of 45 milligrams a day or more may cause gastrointestinal side effects.
A spreadsheet that optimizes for cost per milligram will walk you straight into a dose nobody recommended. If the math is pushing you toward a larger amount than you were originally considering, that’s the moment to stop and ask a clinician or a pharmacist rather than a calculator. The same goes if you take a prescription medication, if you’re pregnant, if you’re buying for a child, or if you started shopping because a lab value looked off.
The other limit is simpler. Cost per milligram of something that doesn’t help you is still wasted money, just more precisely measured. Whether a supplement is worth buying at all is a separate question from what it costs per unit, and we cover that separately in our pieces on evaluating supplement costs and deciding which health purchases are worthwhile.
This is the single habit worth keeping. Before you buy, write down four numbers for each product: the price including shipping, the total units in the container, the units per serving, and the milligrams of the thing you want per serving. Divide the total units by the units per serving to get servings. Multiply that by the milligrams per serving to get the total milligrams in the bottle. Divide the price by that. You now have a figure no front-of-package design can distort, and if you can’t fill in the last number because it’s buried in a blend, you’ve learned something too.
Sources
- PubMed. “Zargar A, Ito MK. "Long chain omega-3 dietary supplements: a review of the National Library of Medicine Herbal Supplement Database." Metabolic Syndrome and Related Disorders, 2011. DOI: 10.1089/met.2011.0004.” doi.org
- CDC National Center for Health Statistics. “Nahin RL, Barnes PM, Stussman BJ. "Expenditures on Complementary Health Approaches: United States, 2012." National Health Statistics Reports No. 95, June 22, 2016.” cdc.gov
- Electronic Code of Federal Regulations (U.S. Government Publishing Office). “21 CFR 101.36, Nutrition labeling of dietary supplements.” ecfr.gov
- U.S. Food and Drug Administration. “Dietary Supplement Labeling Guide: Chapter IV. Nutrition Labeling.” fda.gov
- U.S. Food and Drug Administration. “Dietary Supplement Labeling Guide: Chapter III. Net Quantity of Contents.” fda.gov
- U.S. Food and Drug Administration. “Dietary Supplement Labeling Guide: Chapter VIII. Other Labeling Information.” fda.gov
- NIH Office of Dietary Supplements. “Calcium: Fact Sheet for Health Professionals.” ods.od.nih.gov
- NIH Office of Dietary Supplements. “Vitamin D: Fact Sheet for Health Professionals.” ods.od.nih.gov
- NIH Office of Dietary Supplements. “Vitamin E: Fact Sheet for Health Professionals.” ods.od.nih.gov
- NIH Office of Dietary Supplements. “Iron: Fact Sheet for Health Professionals.” ods.od.nih.gov
- United States Pharmacopeia. “Dietary Supplements Verification Program.” usp.org
- PubMed. “Alsawadi A. "The Perception Filler: A Proposed Conceptual Framework for Ingredient-Interpretation Gaps in Food Supplements." The Journal of Nutrition, 2026. DOI: 10.1016/j.tjnut.2026.101803.” doi.org
- PubMed. “Sikorska-Zimny K, et al. "Preliminary Quality and Safety Evaluation of Lycopene-Based Dietary Supplements: Analysis of Active Compound Content, Microbiological Purity, and Chemical Contaminants." Foods, 2026. DOI: 10.3390/foods15091583.” doi.org