Stim-timing calculator
Log what you drink and when. We run the caffeine through its elimination half-life and show what's left in your system when you train — and when you try to sleep. No account, no email, just the math.
Caffeine remaining
116mg
at workout · 5:00 PM
58mg
at bedtime · 10:00 PM
Sleep readout
You still have roughly 58 mg of caffeine on board at bedtime. In controlled studies, caffeine that close to sleep tends to cut total sleep time for most people — your afternoon dose is the usual driver. Shifting it earlier is the simplest fix.
Total caffeine logged today: 255 mg. The FDA cites 400 mg/day as the figure not generally associated with negative effects for healthy adults.
This is the whole reason we make a stim-free pre-workout. If you already get caffeine from coffee or an afternoon energy drink, you don't need more in your scoop — you need a pump and focus that doesn't add to the number above at 10 PM.
See the stim-free formulaThe science behind the numbers
We don't hide the math behind a brand. Here's where each constant comes from and how confident the research is.
Clinical pharmacology puts the elimination half-life of caffeine near 5 hours in a typical healthy adult. It varies widely by person: smoking speeds it up (~3 hours, via CYP1A2 induction), while pregnancy and oral contraceptives slow it down (often past 10 hours). The slider lets you model your own rate across that 2–12 hour range.
StatPearls — Caffeine pharmacology (NCBI Bookshelf NBK223808) ↗Within normal dietary doses, caffeine clears by first-order kinetics, so remaining amount = dose × (1/2)^(hours elapsed ÷ half-life). That's the exact formula this tool runs — no black box, and you can read it in our source code.
StatPearls — Caffeine pharmacokinetics (NCBI Bookshelf) ↗In a controlled study, 400 mg of caffeine taken even 6 hours before bed cut total sleep time by more than an hour (Drake et al., 2013). We use ~50 mg still circulating at bedtime as a routine-optimization heuristic to color the readout — not a medical threshold, and not a diagnosis of any sleep condition.
Drake et al. 2013, J Clinical Sleep Medicine (PubMed 24235903) ↗The FDA cites 400 mg per day as an amount not generally associated with dangerous, negative effects in healthy adults. Individual tolerance varies; pregnancy and some conditions warrant lower intake.
U.S. FDA — Spilling the Beans on caffeine ↗Preset milligram values are conservative central estimates from USDA/FDA references and common label disclosures. Real products vary — use the custom field with your label's number for precision.
USDA FoodData Central · FDA · manufacturer labels ↗This tool is for general education, not medical advice. It models caffeine in your own reported intake and makes no claims about diagnosing, treating, or preventing any condition. If you have a heart condition, are pregnant, or take medication that interacts with caffeine, talk to a clinician.
