A live BAC tracker for the bar, the wedding, the long Saturday. It runs in your browser. No accounts, no tracking, no servers. Just an honest read on where you're at, and a heads-up before the next drink takes you somewhere you didn't plan to go.
Three things, done well. Built for the moment you start asking yourself "wait, where am I at?"
Tap a drink, watch your BAC rise and fall on a real curve. Nightcap uses the Widmark formula with adjustments for your weight, sex, stomach state, and how long it's been since your last drink — the same approach toxicologists use, just legible.
You see where you are now and where you're heading once everything's absorbed. No surprises an hour later.
Tell Nightcap when you need to drive home, and it'll watch the math for you. The moment one more typical drink would put you over your legal limit by drive time, you get a quiet heads-up — and a one-tap suggestion to extend your drive time if you're staying out longer.
The point isn't to bless driving. It's to make the consequences visible before the choice, not after.
The planner answers the actual question you have at 7pm: "If I'm driving home at 11, how many drinks can I have, and how should I pace them?"
You set the time, pick what you'll be drinking, and Nightcap tells you exactly that — drinks, pacing, projected peak, and what you'll be at when you get behind the wheel. Tight window? You'll know.
Nightcap was built as a tool, not a data product. Everything runs locally in your browser. There is no cloud copy of your night for someone to subpoena, lose, or sell.
No sign-up, no email gate, no password to forget. Open the link and you're in.
Zero analytics, zero pixels, zero third-party scripts. Inspect the source if you want.
Everything lives in your browser's URL. Close the tab, it's gone. Bookmark it, it's yours.
Install it to your home screen. After the first visit, no network needed.
No subscription. No tier wall. No paywall on the safety features. The whole app, every update, forever.
One-time · lifetime updates
Secure checkout via Gumroad. 14-day no-questions refund.
Your purchase keeps Nightcap independent and ad-free.
No, and that's deliberate. Nightcap shows you an estimate of your blood alcohol concentration based on the Widmark formula — the same math used in toxicology. But real BAC varies with food, hydration, medication, genetics, fatigue, and a dozen other factors no app can see. If you've been drinking, don't drive. Nightcap exists to make the consequences visible before the choice, not to bless the choice.
The Widmark formula is a well-validated estimate, not a breathalyzer. Studies consistently put it within ±0.02% BAC of measured values for most people under typical conditions. Nightcap improves on the basic formula by accounting for absorption time (your BAC rises gradually, not instantly) and stomach state (food slows absorption ~15-30%). Treat the number as a useful indicator, not a guarantee.
Most free BAC apps are ad-supported, ask for permissions they don't need, and use a crude version of the formula that ignores absorption time. Nightcap is web-native (works on any phone, any browser, no app store), runs the full math, includes a planner and a driver-warning system, has no ads or trackers, and is built by one person who cares about getting it right. Five dollars buys you no ads, no nags, and a tool that respects you.
No. Nightcap opens like any website. If you want it to behave like a real app — full-screen, on your home screen, working offline — both iOS and Android let you "Add to Home Screen" in your browser's share menu. It's a one-tap install with no App Store involved.
Gumroad emails you a link to the app. Open it, add it to your home screen, you're done. Nothing to sync, no account to set up. The link is yours forever, and every future Nightcap update lives at the same address.
Nowhere. Your sessions are encoded in the URL of the page itself. There is no server-side database, no analytics, no third-party tracker. If you close your browser, the active session ends; if you save it in your history, it stays in your history. We can't see it because we never receive it.
14-day no-questions refund through Gumroad. If Nightcap isn't useful to you, reply to your purchase email and you'll have your $5 back the same day.
A solo developer who got tired of free BAC apps with ads, sketchy permissions, and bad math. Built in the open, designed for harm reduction, priced like a tool. Questions? hello@heynightcap.com.