Who makes it
I'm Inder. I make Onset on my own at Doodle Studio: the app, this website, and the pages that explain how the caffeine estimate works.
This case study describes decisions I made while building Onset. The screenshots show an October 13 development build with demo drinks; the app has changed since then.
The problem
A daily caffeine total leaves out when you had each drink. In Onset's model, a 95 mg coffee at 8 am leaves about 12 mg at 11 pm. The same coffee at 3 pm leaves about 31 mg. So the app has to show the amount and the timing together.
Onset is built around one question: if I have another drink now, how much will still be in my system at bedtime? You can check that before you log anything.
I haven't run a study, so I can't say Onset improves anyone's sleep or changes their habits.
Three design decisions
01 / Preview before saving
Keep a possible drink separate from a logged one.
You can pick a drink and see what it might add before saving it. Logging is a separate step, so you can compare options without filling your history with drinks you never had.
02 / Show the assumption
Use math you can check.
The app and the calculator both use a five-hour half-life and add up what's left of each drink. The calculator explains the formula on the page and works without an account, so you can try the idea before downloading anything.
The downside is precision. One fixed half-life can't match everyone's metabolism, so the app calls its numbers estimates and the guides explain the limits.
03 / Keep it on the phone
Keep caffeine history on the iPhone.
Onset keeps your caffeine history on your iPhone. Apple Health access is optional and read-only. The calculator saves your day in the browser, and a shared link carries the day after the # in the address, which never reaches a server. The privacy policy has the details.
What's shipped
Onset is a free iPhone app on the App Store. Alongside it, this site has the caffeine calculator, four caffeine guides, and support and privacy pages.
The calculator came first, at the end of September. In October I added the guides and gave the apps that aren’t out yet their own page, so Onset is the one finished thing to try.
What I'm learning next
Onset stays free while I work on it and learn from the people using it. What I want to find out:
- Can someone log a drink and preview another without being shown how?
- Do they understand what the caffeine estimate can and cannot tell them?
- Do they choose to come back, and what brings them back?
I don't have numbers on any of that yet. When I do, I'll update this page with what people ran into and what I changed.
If you use Onset, tell me what helped or what confused you. A specific moment, like a screen where you got stuck, helps me more than a star rating.