Caffeine Half-Life: Your Cutoff Time Explained
That 4 p.m. latte isn't "harmless" — it's still half in your system at 10 p.m. Understanding caffeine's half-life turns a vague rule into a number you can actually use.
The half-life math
Caffeine's half-life is roughly 5–6 hours in most people (longer for some, shorter for fast metabolizers or on certain meds). Half-life means the amount halves every ~5–6 hours — so it lingers well past the buzz wearing off.
Find your cutoff
Work backward from bedtime: if you want caffeine near zero by lights-out, stop about 8–10 hours before. A noon cutoff is safe for most; a 3 p.m. cup often costs sleep quality even if you "still fall asleep."
Exceptions and traps
- Decaf isn't zero — it has ~2–5 mg.
- Chocolate and some meds carry hidden caffeine.
- Anxiety and pregnancy lengthen the effective window.
Trade the evening cup for a walk. A short bright-light walk beats a late coffee for the 3 p.m. dip — and protects tonight's sleep.
Not medical advice. If you need large amounts to function daily, it may mask poor sleep rather than cause it — worth addressing the root.