recon-math

The math behind peptide vial reconstitution. Pure TypeScript, zero dependencies.

This library is the calculation engine inside My Pep Calc. We open-sourced the math so anyone can verify it, embed it, or audit it.

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The core formula

Reconstituting a lyophilized peptide vial produces a solution with a known concentration. Every dose you draw is a fraction of that solution.

Concentration (mcg/mL) = Vial strength (mcg) ÷ Bac water added (mL)
Volume to draw (mL)    = Target dose (mcg) ÷ Concentration (mcg/mL)
Units on U100 syringe  = Volume (mL) × 100

Collapsed to one step:

Units = (Target dose ÷ Vial strength) × Bac water volume × 100

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Install

npm install recon-math
# or
pnpm add recon-math
# or
yarn add recon-math

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Usage

import { reconstitute, dosesPerVial, syringeUnits } from 'recon-math';

// Full reconstitution calculation
const result = reconstitute({
  vialStrengthMg: 5,       // vial label: 5 mg
  bacWaterMl: 2,            // you added 2 mL bac water
  targetDoseMcg: 250,       // your target dose: 250 mcg
  syringeType: 'U100',      // U100, U40, or '1mL'
});

console.log(result);
// {
//   concentrationMcgPerMl: 2500,
//   volumeMl: 0.1,
//   syringeUnits: 10,        // draw to the 10-unit mark
//   dosesPerVial: 20,
//   syringeType: 'U100',
// }

// Doses remaining in a vial
const doses = dosesPerVial({ vialStrengthMg: 5, targetDoseMcg: 250 });
// 20

// Convert mL to units for a specific syringe type
const units = syringeUnits({ volumeMl: 0.1, syringeType: 'U100' });
// 10

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Supported syringe types

Type	Units per mL	Use case
U100	100	Standard US insulin syringe — most common for peptides
U40	40	Common in some countries; 40 units = 1 mL
1mL	—	Tuberculin syringe; result returned in mL, not units

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Worked examples

BPC-157: 5 mg vial, 2 mL bac water, 250 mcg dose

reconstitute({ vialStrengthMg: 5, bacWaterMl: 2, targetDoseMcg: 250, syringeType: 'U100' })
// → 10 units

BPC-157: same vial, 1 mL bac water, 250 mcg dose

reconstitute({ vialStrengthMg: 5, bacWaterMl: 1, targetDoseMcg: 250, syringeType: 'U100' })
// → 5 units

Same vial, same dose, half the units — because doubling the concentration halves the draw. This is the most common source of reconstitution errors.

CJC-1295/Ipamorelin blend: 10 mg vial, 2 mL bac water, 400 mcg total dose

reconstitute({ vialStrengthMg: 10, bacWaterMl: 2, targetDoseMcg: 400, syringeType: 'U100' })
// → 8 units

GLP-1 pre-mixed vial: 5 mg/mL concentration, 2.5 mg dose

import { fromConcentration } from 'recon-math';

fromConcentration({ concentrationMgPerMl: 5, targetDoseMg: 2.5, syringeType: 'U100' })
// → 50 units

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API reference

reconstitute(options)

Calculates all values from vial + bac water inputs.

type ReconstitutionOptions = {
  vialStrengthMg: number;     // vial label in mg (e.g. 5 for a 5 mg vial)
  bacWaterMl: number;          // bac water added in mL
  targetDoseMcg: number;       // target dose in mcg
  syringeType: 'U100' | 'U40' | '1mL';
};

type ReconstitutionResult = {
  concentrationMcgPerMl: number;
  volumeMl: number;
  syringeUnits: number | null;   // null for '1mL' syringe type
  volumeMlDisplay: number;        // always populated
  dosesPerVial: number;
  syringeType: 'U100' | 'U40' | '1mL';
};

fromConcentration(options)

For pre-mixed vials where concentration is labeled directly.

type FromConcentrationOptions = {
  concentrationMgPerMl: number;
  targetDoseMg: number;
  syringeType: 'U100' | 'U40' | '1mL';
};

dosesPerVial(options)

Returns total doses from vial strength and dose amount.

dosesPerVial({ vialStrengthMg: number, targetDoseMcg: number }): number

halfLifeAtTime(options)

Returns remaining active mass at time hoursElapsed after a single dose.

import { halfLifeAtTime } from 'recon-math';

halfLifeAtTime({ initialDoseMcg: 250, halfLifeHours: 4, hoursElapsed: 8 })
// → 62.5  (25% remaining after 2 half-lives)

steadyState(options)

Steady-state peak/trough/average for repeated dosing.

import { steadyState } from 'recon-math';

steadyState({ doseMcg: 10000, halfLifeHours: 120, intervalHours: 168 })
// tirzepatide 10mg weekly: peak ~17.7mg, accumulation factor ~1.77×

multiDoseRemaining(options)

Total remaining mass at a given time from a series of past doses (uses superposition).

import { multiDoseRemaining } from 'recon-math';

multiDoseRemaining({
  doses: [
    { hoursFromStart: 0, doseMcg: 250 },
    { hoursFromStart: 4, doseMcg: 250 },
  ],
  halfLifeHours: 4,
  evaluateAtHours: 8,
})
// → 187.5

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Half-life reference

Compound	Half-life	Typical dosing
BPC-157	~4 hours	Once or twice daily
CJC-1295 (no DAC)	~30 minutes	Once or twice daily
Ipamorelin	~2 hours	Once or twice daily
CJC-1295 (with DAC)	~6–8 days	Once or twice weekly
TB-500	~24 hours	Loading/maintenance
Tirzepatide	~5 days	Once weekly
Semaglutide	~7 days	Once weekly

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Disclaimer

This library performs arithmetic. It does not provide medical advice, recommend dosages, or endorse any compound. The user is responsible for confirming inputs (vial strength, bac water volume, target dose) with a licensed healthcare provider before acting on any output.

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Contributing

Issues and PRs welcome. Calculation bugs get priority.

git clone https://github.com/Coolpress/recon-math.git
cd recon-math
npm install
npm test

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License

MIT — see LICENSE.

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Related

• My Pep Calc — the full multi-compound tracker that uses this library
• Reconstitution calculator — web UI for these calculations
• Learn: How to reconstitute a peptide vial — the math explained