I have kept every message, invoice and document, which I gather is the useful habit.
This should be a straightforward calculation and I keep getting two different answers.
The numbers are arbitrary; the method is what I am after.
Can someone show the working rather than just the answer?
Twelve months is 52 weekly administrations across 365 days, and on a four-week ladder from the bottom of the range about 5 steps — so roughly 20 of the 52 doses are escalation doses and 32 are at maintenance. Model it in that order and the routes become comparable: doses per year first, milligrams per dose second, cost per milligram third. Anything quoted per vial hides the second of those, which is the one that changes most between the first 20 doses and the last 32. Then add what each route charges that the other does not. A prescription route carries consultation and dispensing fees, spread across the 52 doses rather than paid once. A research route carries testing, shipping, and the material lost between them. Testing is the line most sheets omit. At one lot a quarter, a test-every-lot policy is 4 assays a year; at one lot a month it is 12. That difference is usually larger than any difference in price per milligram, and it is a policy you choose rather than a cost you are quoted. Put doses per year in the top row and derive everything under it, and the twelve-month totals compare on arithmetic instead of on presentation.
The short version: unit price, carriage, testing, dead-space loss and wastage. The first is the one everybody compares and rarely the one that decides it.
Wastage from a reconstituted vial discarded at the end of its in-use period is a genuine cost, and it is a function of the diluent volume chosen at reconstitution rather than of anything the supplier did.
| Step | Value | Note |
|---|---|---|
| Vial price, 10 mg nominal | £34.00 | As advertised |
| Nominal cost per mg | £3.40 | 34 ÷ 10 |
| Measured content | 9.2 mg | Independent content assay |
| Cost per actual mg | £3.70 | 34 ÷ 9.2 |
| Dead-space loss, 20 draws | 4 % | 80 µL of a 2 mL fill |
| Cost per delivered mg | £3.85 | 3.70 ÷ 0.96 |
| First vial, with £110 assay | £14.85 | Testing dominates a single vial |
Carriage amortises across the order. Twenty-five pounds of carriage on one vial is £2.50/mg on a 10 mg vial; on ten vials it is £0.25/mg. That single term explains most of the case for larger, less frequent orders.
Published content assay results across the independent services show nominal and measured content differing by one to ten per cent, which is the term that makes label-price comparisons unreliable.
A spreadsheet built on label claim rather than measured content is precise about the wrong number.
Divide by measured content, not by label claim. That is the whole correction.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThis is a spreadsheet question and doing it properly changes conclusions more often than people expect.
Change one number and it reverses: if B assays at 82 per cent, that is 8.2 mg for £52, or £6.34/mg, and the cheaper vial is now the more expensive peptide.
Concretely, independent testing costs roughly the price of one to two vials at the services this community uses. On a two-vial order that is a fifty to a hundred per cent surcharge; on a twenty-vial order it is five per cent.
Syringe dead-space volumes are published per design, with fixed-needle insulin syringes under 5 microlitres and conventional luer designs at 35 microlitres or more.
Fixed-needle syringes save more peptide than most price differences do.
edited 19 Apr 2026 by petra_hovland — clarified the distinction between purity and content
Answer first: compare cost per milligram of measured peptide, not per milligram of label claim, because content varies enough to reverse a comparison.
Worked example. Supplier A: £60 for a 10 mg vial, content 96 per cent, so 9.6 mg for £60, or £6.25/mg before carriage. Supplier B: £52 for the same nominal vial, content 88 per cent, so 8.8 mg for £52, or £5.91/mg. B still wins here, but the gap has narrowed from thirteen per cent on the label to five per cent in reality.
The part that matters: cost per milligram is the wrong metric entirely if you are optimising for confidence rather than price, and it is worth saying which one you are doing before you build the spreadsheet.
Larger orders reduce cost per milligram and increase exposure to a single lot, which is a real trade rather than a free win.
Decide whether you are optimising cost or confidence before you build the model.
Testing cost per milligram falls sharply with order size, which is the main argument against very small repeat orders.
The full calculation: (unit price + carriage share + testing share) ÷ (nominal mg × measured content fraction × (1 − dead-space and wastage fraction)). Every term after the first is routinely omitted.
Carriage on international consignments scales sub-linearly with weight, which is the quantitative basis for order consolidation.
Larger orders are cheaper per milligram and concentrate lot risk. Price both.
Wastage from expired reconstituted vials is a real line item and nobody includes it.
Dead-space loss is small with fixed-needle insulin syringes — a few microlitres per draw — and substantial with detachable-needle luer syringes at 35 to 100 microlitres. Across twenty draws that is up to two millilitres of solution.
Independent testing prices at the services this community uses are published and are stable enough to model.
Include carriage and testing as per-milligram terms. They dominate small orders.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.