RoastMojo — a caffeine half-life calculator that shows how long your coffee, tea, and energy drinks stay in your system
How much caffeine is still buzzing through your system?
What's this?
Log what you drank and when, and RoastMojo adds up each drink's caffeine decay to show your combined level over time. The math:C(t) = C₀ · (0.5)^(t / 5.7), using caffeine's average 5.7-hour biological half-life, summed across everything you've logged.
What did you drink?
Tap a drink to log it — tap it again if you're having another.
Your log
Your caffeine level
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Buy me a Coffee (~63mg)Frequently asked questions
What does "half-life" mean here?
Caffeine's half-life is how long it takes your body to clear half of what you drank. We use 5.7 hours, a commonly cited average for healthy adults: C(t) = C₀ · (0.5)^(t / 5.7), where C₀ is a drink's caffeine dose and t is hours since you had it.
Why 5.7 hours specifically?
It's a population-average figure from caffeine pharmacology research. Your actual half-life can run anywhere from about 3 to 7 hours depending on genetics, liver function, pregnancy, smoking, medications, and other factors — so treat the curve as a solid ballpark, not a personalized measurement.
How do multiple drinks combine?
Each logged drink decays on its own independent curve starting from when you had it. The number and chart you see are the sum of every active curve at that moment — so a cortado at 1pm on top of a lingering espresso from 10:30am shows up as their combined total, not just the most recent drink.
Can I log a drink from earlier today, not just right now?
Yes — tap the time next to any logged drink and change it. In this first version all entries are assumed to be from today; there's no way yet to log something from yesterday.
How accurate are the caffeine-content numbers?
They're typical published averages for a standard serving of each drink — actual caffeine content varies a lot by brand, brew strength, and serving size. This tool is for fun and general awareness, not medical or nutritional advice.