Caffeine Half-Life Calculator
Calculate your active bloodstream caffeine level at bedtime using pharmacokinetics.
Caffeine Intake & Bedtime
Bloodstream Decay Curve (24-Hour Timeline)
Sleep Architecture Impact & Toxicity Safety
⚖️ Decision Verdict: Delayed Sleep & Fragmented Deep Rest Likely
Because you consumed an energy drink at 2:00 PM, an estimated 61.9mg of active caffeine remains bound to adenosine receptors in your brain at 10:30 PM bedtime. Even if you fall asleep from sheer exhaustion, research shows residual caffeine significantly reduces restorative Stage 3/4 non-REM deep sleep. For deep, restorative sleep, set your daily caffeine cutoff to 1:30 PM.
About this tool
How to use it
- Select your metabolism speed (average adult half-life is 5 hours; oral contraceptives or pregnancy extend this to 6.5–8 hours).
- Choose your morning and afternoon drinks (drip coffee, espresso, cold brew, energy drink, matcha, diet cola, pre-workout).
- Enter the exact time you drank each beverage and your planned bedtime tonight.
- Inspect the interactive 24-hour bloodstream exponential decay curve and your recommended caffeine cutoff time.
- Review your estimated bedtime caffeine level against the 25mg sleep disruption threshold.
Why it matters
Caffeine has an average elimination half-life of 5 hours, meaning 25% of the drug is still circulating in your body 10 hours after consumption. Because caffeine functions as an adenosine receptor antagonist, bedtime levels above 25mg to 50mg block natural sleep pressure and suppress restorative slow-wave deep sleep.
When to use it
Use this calculator when deciding whether to drink an afternoon espresso, diagnosing morning grogginess despite 8 hours in bed, or establishing a healthy evening wind-down routine.
Good to know
Medical Notice: Even if you can fall asleep easily after late-night coffee, clinical polysomnography studies show caffeine significantly fragments sleep architecture and decreases restorative Stage 3 and Stage 4 delta-wave sleep.
Common questions
What is caffeine half-life?
Half-life is the duration required for your liver (specifically the CYP1A2 enzyme) to eliminate 50% of the circulating caffeine from your bloodstream. In healthy non-smoking adults, caffeine half-life averages between 4 and 6 hours.
Why can I fall asleep fine after late-night coffee?
Falling asleep (sleep latency) is only one facet of sleep. Research in sleep medicine demonstrates that even when participants fall asleep quickly, bloodstream caffeine decreases slow-wave deep sleep by up to 20% to 30%, causing brain fog and fatigue the following morning.
What is the optimal caffeine cutoff time?
For most adults with an average 5-hour half-life who go to bed at 10:30 PM, stopping all caffeine intake by 1:30 PM to 2:00 PM ensures residual levels drop below the 25mg threshold by sleep time.
What factors slow down caffeine metabolism?
Oral contraceptives double caffeine half-life (up to 8–10 hours). Pregnancy substantially slows clearance (up to 15+ hours in the third trimester). Conversely, cigarette smoking induces the CYP1A2 enzyme and speeds up clearance.
What is the FDA maximum daily caffeine limit?
The US Food and Drug Administration (FDA) recommends a maximum daily intake of 400 milligrams of caffeine (roughly 4 to 5 cups of brewed coffee) for healthy adults, which is generally not associated with adverse cardiovascular or neurological effects.