ARC for Coffee Drinkers
A caffeine tracker for Coffee Drinkers
Know your last safe coffee. ARC works it out from your bedtime, your caffeine sensitivity and every drink you log, aiming for under 50 mg at bedtime.
Download on theApp StoreThe Problem
- ✕Afternoon energy crashes despite drinking coffee
- ✕Difficulty falling asleep on days you have late coffee
- ✕Not knowing how much caffeine is still active at bedtime
- ✕Guessing whether one more cup is OK
How ARC Helps
ARC treats caffeine as a curve, not a rule. It asks whether you clear caffeine fast, average or slow (a half-life of about 4, 5.5 or 7 hours), tracks every drink you log, and tells you plainly when no cup fits before bed.
Key Features
- ✓Live caffeine decay curve
- ✓Last safe coffee, recalculated with every drink
- ✓Cutoff widget for your Home and Lock Screen
- ✓Drink logging by type
How the Cutoff Works
There's no universal cutoff. For one average cup and an average metaboliser, caffeine takes roughly five hours to fall below 50 mg; a bigger cup, a slower metabolism, or an earlier coffee still in your system pushes that earlier. ARC works it out from your bedtime, how fast you clear caffeine, and everything you've logged today.
The cutoff has three states: a countdown while you're ahead, passed once the time has gone, and no cup fits when even a small drink would still be above 50 mg at bedtime. The caffeine half-life guide goes through the math, and when to stop drinking coffee covers the everyday version.
Why Coffee Sometimes Makes You More Tired
Caffeine blocks adenosine receptors; it doesn't clear adenosine. When it wears off, the tiredness that built up in the meantime comes back. More on that in why coffee makes you tired.
ARC won't tell you to quit. If you want to lower your tolerance, our 7-day caffeine tolerance reset is a step-down plan you can log in ARC as you go.
Calculate Your Live Caffeine Decay
Enter your bedtime and today's drinks to see how much caffeine will still be circulating when you go to bed.
Questions from Coffee Drinkers
Is the 50 mg target a medical threshold?▼
No. It's a conservative target ARC uses so that little caffeine is left at bedtime. Sensitivity varies, which is why ARC asks how fast you clear caffeine.
Is caffeine half-life the same for everyone?▼
No: roughly 4 to 7 hours depending on the person (around 5 on average). Pregnancy and some medications can slow it considerably, and smoking speeds it up. If you're pregnant, ask your doctor or midwife about caffeine limits.
Where is my data stored?▼
Your log stays on your iPhone. No account. The one exception is the daily sentence: to write it, ARC sends a short timing summary (wake time, bedtime, dip time and today's caffeine) to a language model.