Caffeine half-life calculator
How much of that coffee is still in your system at bedtime — and when your last cup actually wears off.
Caffeine doesn't leave when the buzz does. With a half-life of around five hours, half of your afternoon coffee is still circulating at dinner and a quarter of it at midnight. Pick your drink, your metabolism speed, and how long until bed, and this calculator shows the milligrams that will still be working against your sleep.
Drip · 145 mg dose · 5 h half-life
At bedtime
47
mg still in your system
Of the dose
33%
remaining
145 mg drunk 8 h before bed ≈ 47 mg still circulating at lights-out — under the ~50 mg level most sleep research considers negligible.
The average healthy adult clears half of a caffeine dose in about 5 hours.
Love the evening cup, not the 2 a.m. ceiling?
The fix isn't quitting the ritual — it's switching the cups inside your cutoff window to a decaf good enough that you don't notice.
Kicking Horse Decaf Whole Bean Coffee
A Swiss Water decaf with real body and chocolate notes — decaf that doesn't taste like a compromise.
Check price on AmazonVolcanica Colombian Swiss Water Decaf
A bright, clean single-origin decaf for people who want flavor, not just the absence of caffeine.
Check price on AmazonHow caffeine actually decays
With a typical 5-hour half-life, here's what happens to one 8 oz cup of drip (95 mg) over the day.
| Time since coffee | Dose remaining | Of a 95 mg cup |
|---|---|---|
| Right after drinking | 100% | 95 mg |
| After 2.5 hours | 71% | 67 mg |
| After 5 hours | 50% | 48 mg |
| After 7.5 hours | 35% | 34 mg |
| After 10 hours | 25% | 24 mg |
| After 15 hours | 12.5% | 12 mg |
| After 20 hours | 6% | 6 mg |
Read on
Common questions
How long does caffeine stay in your system?
Caffeine has a half-life of about 5 hours in the average healthy adult, so half of your dose is still circulating 5 hours later, a quarter after 10 hours, and an eighth after 15. A 95 mg cup of drip at noon still leaves roughly 25 mg in your system at 10 pm — and genetics, smoking, pregnancy, and some medications can swing that half-life from under 4 hours to well over 9.
What does caffeine half-life mean?
Half-life is the time your body needs to eliminate half of the caffeine you consumed. It compounds: after one half-life 50% remains, after two 25%, after three 12.5%. That's why a late-afternoon coffee lingers into the night — elimination slows to a trickle in absolute terms, but the tail is long.
When should I stop drinking coffee before bed?
A common evidence-based rule is to stop caffeine 8 to 10 hours before bedtime. Studies show 400 mg taken even 6 hours before bed measurably disrupts sleep. If you're aiming to be under about 50 mg at lights-out, a typical metabolizer should have their last full-strength cup by early afternoon — or switch the later cups to decaf.
Does decaf coffee affect sleep?
Rarely. Decaf carries only 2–5 mg of caffeine per cup — around 3% of a regular cup — so even an after-dinner decaf leaves a negligible amount in your system at bedtime. A good Swiss Water decaf is the standard move for evening coffee without the 2 a.m. ceiling-staring.