Caffeine Cutoff Calculator
Updated for 2026 · All math runs privately in your browser
That 4 PM coffee is still in your blood at midnight. Enter your bedtime to find your last safe coffee — and watch a timeline of caffeine decaying in your body through the day.
Your day
8–10 hours is the research-backed range. Sensitive sleepers: use 10+.
We'll show how much of it is still in you at bedtime.
Your caffeine cutoff
Your day, caffeinated
- Bedtime—
- Your last coffee—
- Caffeine half-life used~5.5 hours
- Still in you at bedtime—
Decay math uses caffeine's average 5.5-hour half-life. Slow metabolizers (and many medications) stretch it longer — when in doubt, cut off earlier.
How to use this calculator
- Enter your bedtime — when you actually try to sleep.
- Set your caffeine-free window (8 hours is the standard recommendation).
- Enter when you had your last coffee to see how much is still in your system at bedtime.
- Read the timeline: green is safe, amber means the cutoff is near, red will cost you deep sleep.
How the math works
Cutoff time = bedtime − caffeine-free hours. Bed at 11:00 PM with an 8-hour window → last coffee at 3:00 PM.
Caffeine remaining uses exponential decay with a 5.5-hour half-life: remaining = 100% × 0.5(hours until bed ÷ 5.5). A 2:00 PM coffee leaves ~25% still circulating at an 11:00 PM bedtime.
The timeline paints your day from 6:00 AM to bedtime: green while coffee is safe, amber in the final hour before cutoff, red after — the hours when caffeine measurably shrinks deep sleep.
Frequently asked questions
Caffeine's half-life is about 5–6 hours in most adults: half of it is still in your blood 5–6 hours after your last sip, and a quarter can linger after 10–12 hours. That's why an afternoon coffee can still be working at midnight.
Sleep researchers commonly recommend a cutoff 8–10 hours before bedtime. If you sleep at 11 PM, your last coffee should be around 1–3 PM. The calculator defaults to 8 hours; heavy caffeine metabolizers can use 6.
Yes — studies show caffeine before bed reduces deep slow-wave sleep and total sleep time even in people who fall asleep fine. You sleep, but it's lighter, more fragmented sleep.
Drink a coffee and immediately take a 20-minute nap. The nap clears early sleepiness while the caffeine kicks in right as you wake — research shows the combo beats coffee or napping alone for alertness.
Much less: decaf still contains 2–7 mg of caffeine per cup versus ~95 mg in regular coffee. For most people an evening decaf won't meaningfully affect sleep.
About 95 mg per 8 oz brewed cup, ~150 mg for a 12 oz, and 200+ mg in many energy drinks. Espresso shots run ~63 mg each. The calculator's decay math assumes a standard cup.