PepCalc
A private, offline peptide reconstitution and draw calculator for researchers. Install it
from the browser to your phone or tablet's home screen; it then works with no connection.
Everything you enter stays on your device.
Pick a peptide, the amount in your vial and the water you added, and PepCalc shows how far to
draw the syringe, with a drawing of the barrel to check against. It runs on your device with no
account, server or tracking.
PepCalc does arithmetic and shows sourced reference values. It does not recommend doses and
is not medical advice. Several listed peptides are investigational or not approved for human
use.
Features
- Draw calculator: dose in mg, mcg or IU, with the volume and syringe reading for U-100 (1,
0.5, 0.3 mL, half-unit), U-40 and mL syringes. Warns when a draw is over capacity, under one
mark or between marks.
- Mixing advisor: enter the doses you plan to draw and your vial size, and PepCalc ranks water
volumes so every dose fits one syringe and lands on a mark. For peptides users report as
stinging (GHK-Cu and blends that contain it), it dilutes as far as the vial allows, or says how
far to top up the syringe with water.
- Presets with sources: vial sizes, water volumes and doses for each peptide, each marked as
coming from a prescribing label, a clinical trial or community reports.
- Blends: KLOW, GLOW and custom mixes split each dose into its components.
- Shelf: save mixed vials, log draws and see what's left.
- Level charts: an estimate of the amount remaining in the body, based on a simple model from
published human data (semaglutide, tirzepatide, retatrutide, cagrilintide, tesamorelin). For
other peptides you can enter your own half-life, and the chart is marked user-supplied.
- Share and export: share a level chart as an image, with or without the peptide name and
amounts, or export a PDF report for the last 30 days, 90 days or all time. Both are made on
the device.
- Private and offline: no account, server, analytics or third-party requests. Back up to a JSON
file you keep.
- Phones and tablets, in light and dark themes.
Launch peptides
Semaglutide, Tirzepatide, Retatrutide, Cagrilintide, Tesamorelin, BPC-157, TB-500, GHK-Cu, KPV,
GLOW, and KLOW. Adding more is a data change: see docs/adding-a-peptide.md.
How the numbers work
- Concentration = amount in vial / water added.
- Volume to draw = dose / concentration.
- Syringe reading = volume x units per mL (100 for U-100, 40 for U-40), or mL directly.
- Mixing advisor: tries water in 0.5 mL steps up to 10 mL, keeps volumes where the largest
dose fits one syringe and the smallest is at least one mark, then ranks by fitting the vial,
meeting any comfort cap (mg/mL), landing on marks, and most water.
- Level chart: a one-compartment model with first-order absorption and elimination, fitted to
the published half-life and time to peak and summed over doses. It estimates drug remaining
in the body, not blood concentration.
Installing on a device
Settings shows the steps for the browser you are using, with a screenshot.
| Device | Steps |
|---|
| Android, Chrome or Edge | Menu, Install and create shortcut (or Add to Home screen) |
| Android, Firefox | Menu, Add app to Home screen |
| iPhone or iPad, Safari | Share, Add to Home Screen |
| iPhone or iPad, Chrome | Share (in the address bar), Add to Home Screen |
On iPhone and iPad, Safari and the installed app keep separate data; use a backup to move it.
Make regular backups (Settings): browsers can clear site data under storage pressure.
Development
Requires Node 24 (see .nvmrc).
nvm use
make install
make dev # http://localhost:5173/app/
make check # fast gate
make check-all # full gate, including offline e2e tests
Project conventions for contributors and coding agents are in CLAUDE.md and
.claude/skills/.
Deploying to GitHub Pages
This repository is PepCalc/app, so Pages serves it at
pepcalc.github.io/app. The website at the root of the same
origin is the separate PepCalc/pepcalc.github.io
repository.
- In the repository settings, under Pages, set the source to GitHub Actions.
- Push to
main. .github/workflows/deploy.yml runs the gate, builds with the repository
name as the base path (/app/), and publishes.
With a custom domain on the website repository, the app stays at /app/ on that domain; set
the repository variable PEPCALC_SITE_URL to the new root (for example https://pepcalc.app/)
so the canonical tags and share cards name it. A new domain is a new origin, so data saved at
pepcalc.github.io does not follow: users move it with a backup file.
Android app
The Android app is a Capacitor shell around the same web build,
bundled into the APK so it works offline from first launch. It requests no network permission;
CI fails if the merged manifest ever asks for one. Cloud backup is off, so data leaves the
device only as a backup file the user exports.
make android # build dist-android/ and sync it into android/
cd android && ./gradlew assembleDebug # needs JDK 21 and the Android SDK
.github/workflows/android.yml builds a debug APK on every push and uploads it as a workflow
artifact. .github/workflows/release.yml builds a signed App Bundle (Google Play) and APK on a
v* tag and attaches both to a GitHub release. A release build is signed when PEPCALC_KEYSTORE, PEPCALC_KEYSTORE_PASSWORD,
PEPCALC_KEY_ALIAS and PEPCALC_KEY_PASSWORD are set; keep the keystore out of the
repository and backed up, because a lost key means the app can never be updated. The version
comes from package.json (versionCode is major * 10000 + minor * 100 + patch).
The app id io.github.pepcalc.app, and the WebView origin https://localhost that holds the
app's IndexedDB, must never change after release. Data in the browser-installed PWA does not
carry over to the Android app (and vice versa); move it with a backup file.
npm run icons:android regenerates the launcher icons from public/favicon.svg.
iOS app
The iOS app is the same Capacitor shell (Swift Package Manager, no CocoaPods), built only in
GitHub Actions since there is no Mac. make ios builds dist-ios/ and syncs it into ios/;
.github/workflows/ios.yml builds it for the simulator on every push, and on a v* tag (or
run by hand) archives a signed build and uploads it to App Store Connect for TestFlight. Its
WebView origin, capacitor://localhost, must never change after release.
npm run icons:ios regenerates the app icon and launch image from public/favicon.svg.
The release checklist, signing, Google Play, F-Droid and App Store setup are in
docs/releasing.md.
