Price per milligram explained: the arithmetic, worked on real 2026 prices, and when it misleads

Price per milligram is the one number that lets you see through a price ladder. It is also the number most often used to compare things that are not comparable. Here is the arithmetic, worked on the prices published on September 4, 2026, and then the limits.

The formula

For a brand fill: price per fill, divided by the number of doses in the fill, divided by the milligrams in each dose.

A Zepbound KwikPen or four vials at 5 mg: $399 per fill, four doses, 5 mg each. Per dose: $399 / 4 = $99.75. Per milligram: $99.75 / 5 = $19.95. Or in one step: $399 / (4 x 5) = $19.95.

For a compounded vial: price per vial divided by total milligrams in the vial, which you read from the pharmacy label as concentration times volume (a 10 mg/mL vial of 2.5 mL holds 25 mg). $299 for 25 mg is $11.96 per mg. Add fees, shipping and any unused remainder and you get an all-in per-mg figure that is higher; the calculator reports both.

Worked: the Zepbound ladder

The same product is four times cheaper per milligram at the top of the ladder than at the bottom, because the price rises by half while the drug quantity rises sixfold. This is the normal shape of GLP-1 pricing and it is why a per-mg number without the strength attached is meaningless.

Worked: flat pricing

Mounjaro self-pay is $499 at every strength on TrumpRx.gov, so per mg it runs from $49.90 (2.5 mg) to $8.32 (15 mg). Wegovy is $349 at 0.25 through 2.4 mg: $349 per mg at the starting strength, $36.35 per mg at 2.4 mg. The starting-strength per-mg figures look absurd, and they are the price of a four-week ramp, not a price anyone pays for long.

Worked: pen versus pill

The Ozempic 2 mg pen is $499 per fill for 8 mg: $62.38 per mg. The Ozempic pill at 9 mg is $299 per 30 tablets for 270 mg: $1.11 per mg. That does not make the pill fifty times better value. Oral semaglutide has low bioavailability and its tablets are dosed in milligrams that are not equivalent to injected milligrams; the FDA approved the new tablet strengths on bioequivalence to the old ones, not to the pen. Per-mg comparisons across routes compare nothing.

The fill-length correction

A 28-day fill happens 13.04 times a year (365.25 / 28), not 12. "$449 a month" is $5,853 a year, which is $488 per calendar month; the per-month quote understates the year by 8.7 percent. A 30-tablet bottle is 12.18 fills a year, a 1.5 percent understatement. Per-mg and per-dose figures are not affected by this; only the monthly and annual totals are. The calculator uses 365.25 / 12 days as a month for brand fills and 52 / 12 weeks for compounded weekly dosing, and shows the drift.

When per-mg misleads

1. Across molecules. Tirzepatide, semaglutide, liraglutide and orforglipron have different potencies and dosing; a milligram of one is not a milligram of another. A per-mg figure across Zepbound and Wegovy is arithmetic without meaning.
2. Across routes. Injected and oral milligrams are not the same, as above.
3. Across approved and compounded products. A compounded vial's stated concentration is the pharmacy's claim about its own preparation, not an FDA-reviewed label, and the FDA has documented dosing errors with compounded semaglutide where units, milligrams and millilitres were confused. A per-mg figure is only as reliable as the milligram figure it divides by. The comparison page takes this further.

When it is useful

Within one product, per-mg shows where the price ladder is steep and where it is flat. Within one compounded provider, it shows whether a higher-concentration vial is priced in proportion. Between two quotes for the same compounded molecule at the same concentration from the same kind of pharmacy, it is the fair comparison, provided you compare all-in figures with the same fees inside. That is the case the calculator is built for.