The "no coffee after 2pm" rule is everywhere, but it's a rough approximation, not a precise one — and for a lot of people, it's actually too generous, letting caffeine linger further into the evening than they realize.
Caffeine's half-life — the time it takes your body to clear half of what you consumed — is typically 5 to 6 hours, but that's an average, not a fixed number that applies equally to everyone. It varies meaningfully based on genetics, liver enzyme activity, certain medications, and even factors like pregnancy, which can significantly slow caffeine metabolism. Some people clear caffeine noticeably faster than average; others, noticeably slower, sometimes by a factor of two or more.
Here's the part most caffeine advice conveniently skips: even after that first half-life passes, you haven't cleared the caffeine — you've cleared half of it. A coffee consumed at 2pm still has a real, measurable amount of caffeine circulating in your system at 8pm, even for someone metabolizing at an "average" rate. For someone on the slower end of that range, that residual caffeine can still be meaningfully affecting sleep onset well past midnight, long after they've stopped consciously associating their restlessness with an afternoon coffee.
What actually determines your real cutoff is less about a universal clock time and more about working backward from your actual bedtime. A reasonable, more honest rule of thumb is stopping caffeine at least 8 to 10 hours before you plan to sleep — which, for someone with a 10 or 11pm bedtime, often means early-to-mid afternoon at the latest, not the commonly cited 2pm flat cutoff that ignores individual bedtime entirely.
One thing worth knowing separately, and rarely mentioned: caffeine doesn't just delay falling asleep. Some research suggests it can reduce deep sleep specifically, even in cases where it doesn't feel like it's keeping the person awake at all. That means you can fall asleep at a perfectly normal time, feel like caffeine "didn't affect you," and still be getting measurably lower-quality rest without ever connecting the two.