Calculator Tools
Caffeine Calculator
Track caffeine in your system with a half-life decay model. See current mg, hourly timeline, and when levels drop low enough for sleep.
Add a drink
Pick a common drink or enter a custom caffeine amount. Set how many hours ago it was consumed. Drinks just consumed use 0.
Tracked drinks
Each row contributes to the timeline. Remove any drink to see the curve update instantly.
Brewed coffee, 12 oz cup
140 mg consumed 2 h ago. About 106 mg still active.
Brewed coffee, 8 oz cup
95 mg consumed just now. About 95 mg still active.
Next 24 hours
Hour-by-hour caffeine level projected from now, using a half-life of 5 hours.
| Hour from now | Caffeine | Level |
|---|---|---|
| +0 h | 201 mg | |
| +1 h | 175 mg | |
| +2 h | 152 mg | |
| +3 h | 133 mg | |
| +4 h | 116 mg | |
| +5 h | 101 mg | |
| +6 h | 88 mg | |
| +7 h | 76 mg | |
| +8 h | 66 mg | |
| +9 h | 58 mg | |
| +10 h | 50 mg | |
| +11 h | 44 mg | |
| +12 h | 38 mg | |
| +13 h | 33 mg | |
| +14 h | 29 mg | |
| +15 h | 25 mg | |
| +16 h | 22 mg | |
| +17 h | 19 mg | |
| +18 h | 17 mg | |
| +19 h | 14 mg | |
| +20 h | 13 mg | |
| +21 h | 11 mg | |
| +22 h | 9.5 mg | |
| +23 h | 8.3 mg | |
| +24 h | 7.2 mg |
How the math works
Caffeine clears the body through first-order pharmacokinetics. After one half-life, half the dose remains. After two half-lives, a quarter. After three, an eighth. The model used here is remaining = dose × 0.5^(hours / halfLife). Doses across the day are summed because caffeine is additive in the bloodstream within the typical dose range. The default half-life of 5 hours reflects the middle of the commonly cited 3 to 7 hour adult range. Individual variation is significant: smokers metabolize caffeine roughly twice as fast, pregnancy can extend the half-life to 10+ hours, and CYP1A2 genotype meaningfully shifts both.
This tool is for education and planning, not for medical advice. The drink presets use widely reported average values; brewing strength and serving size vary. The FDA describes 400 mg/day as the level most healthy adults can consume without negative effects, but tolerance varies. Pregnant people, anyone managing heart conditions or anxiety, and anyone on medication should talk to a clinician about caffeine.
How to use
- Pick a drink from the preset list or choose Custom and enter its caffeine in milligrams.
- Enter how many hours ago you drank it. Use 0 for just now, 0.5 for thirty minutes ago, and so on.
- Click Add drink. Repeat for every coffee, tea, soda, energy drink, or pre-workout you've had today.
- Adjust the half-life slider if you metabolize caffeine faster (smokers) or slower (pregnancy, oral contraceptives).
- Read the current level, the next-24-hour timeline, and the sleep-safe timing rows. Use Copy summary to save the result.
About this tool
Caffeine Calculator estimates how much caffeine is in your system right now and how much will remain over the next 24 hours using a first-order half-life decay model: remaining = dose × 0.5^(hours / halfLife). Add one or more drinks from a preset list of common coffees, teas, sodas, energy drinks, pre-workouts, and chocolates, or enter a custom milligram amount. Set how many hours ago each drink was consumed, and tune the half-life from 3 to 7 hours to reflect your own metabolism. The tool reports your current caffeine level, your total intake for the day, an hour-by-hour projection for the next 24 hours, and the time until your level drops below the 50 mg and 25 mg sleep-safe thresholds and the ~6 mg practical clearance level. A daily reference compares your intake to the FDA's up-to-400 mg/day guideline for healthy adults. All math runs locally in your browser; nothing is uploaded.
Free to use. Works in your browser. No signup, no login.
Related tools
You may also like
Water Intake Calculator
Personalized daily water target with mL, L, fl oz, cups, glasses, and an hourly schedule.
Open tool
CalculatorSleep Calculator
Plan bedtime or wake up time around full 90-minute sleep cycles.
Open tool
CalculatorTDEE Calculator
Daily calorie needs and BMR with cut, maintain, and bulk goal targets.
Open tool