"No coffee after 5" is folk wisdom. Whether it is right for you depends on arithmetic — how much caffeine you drink, when, and how fast your body clears it. This guide gives you the numbers and a two-minute calculation.
The half-life math
Caffeine's average half-life is about five to six hours: five to six hours after your cup, half the caffeine is still circulating. So a 200 mg mug at 3 p.m. leaves roughly 100 mg in your blood at 8–9 p.m. and about 50 mg after midnight — 50 mg is about half an espresso, sipped while you are trying to fall asleep.
The number that matters even more for sleep is the quarter-life: the time until three-quarters is cleared, roughly ten to twelve hours. If you sleep at 11 p.m., a quarter of your noon coffee is still on board at bedtime. That is why some sleep researchers put the honest cutoff for sensitive people at lunchtime, not late afternoon.
How much is actually in your cup
- Drip or pour-over coffee (250 ml): roughly 90–120 mg
- Single espresso shot: roughly 60–75 mg — a latte with two shots beats a small drip coffee
- Instant coffee (250 ml): roughly 60–80 mg
- Black tea (250 ml): roughly 40–50 mg; green tea 25–35 mg
- Cola (355 ml can): roughly 30–40 mg
- Energy drinks: commonly 80–160 mg per can — check the label
- Dark chocolate (50 g): roughly 20–30 mg
- Decaf coffee: not zero — typically 2–7 mg per cup, which matters if you drink three
For reference, the U.S. FDA treats up to about 400 mg per day as a level generally not associated with negative effects for healthy adults. Pregnancy, some medications, and heart conditions lower that ceiling — ask your doctor, not a blog.
Calculate your personal cutoff
1. Add up a normal day's intake using the list above. Most people who "only have two coffees" land between 250 and 350 mg once the afternoon latte and the cola are counted. 2. Take your usual bedtime and subtract ten hours. That is your quarter-life-based cutoff — the last time a full-strength coffee can clear enough to leave sleep mostly alone. Bedtime 11 p.m. → cutoff 1 p.m. 3. If you fall asleep fine but wake at 3 or 4 a.m., treat that as caffeine's signature too. It shortens deep sleep in the first half of the night even when it does not stop you falling asleep — you can be "able to sleep after espresso" and still be sleeping worse.
Why you stopped feeling it (and still should not trust it)
Caffeine works by blocking adenosine, the molecule that accumulates while you are awake and makes you sleepy. Drink daily and your brain compensates by adding adenosine receptors — that is tolerance. The alertness kick shrinks, but the sleep disruption largely does not, because the caffeine is still in the receptors' way at night. "It doesn't affect me anymore" usually means "it no longer feels like anything," not "it no longer does anything."
If you want to cut down without the headache
Quitting cold turkey earns most daily drinkers a withdrawal headache and two or three foggy days. A gentler taper: replace one daily drink at a time, at three-to-four-day intervals — afternoon coffee to black tea, then black tea to green or decaf. In under two weeks you can halve your intake without a single bad day, and the first thing most people notice is not the mornings — it is that the 3 a.m. wake-ups stop.