How much caffeine is still working in you.

And how late you can drink and still fall asleep tonight.

Most trackers count the cups you drank. Cira counts what is left. Caffeine climbs for about forty-five minutes, then leaves at a rate set by your own metabolism — smoking, contraceptives, pregnancy, age — not by an average adult. Between a fast metabolism and a slow one the difference is hours of sleep.

What it tells you

• Active caffeine right now, in milligrams
• The hour after which a normal cup starts costing you sleep
• Whether tonight holds, and when you will be clear
• Today's whole curve: where the peak was and where it goes next

Everything you log stays on your iPhone. There is no account.