Caffeine, explained
Why can't I sleep even though I stopped caffeine at 2pm?
The no-caffeine-after-2pm rule does not work for everyone, and there is a real reason why.
The rule everyone gives you
"Just stop drinking coffee by 2pm" is probably the most repeated piece of sleep advice there is. It is also wrong for a lot of people, not because the logic is bad, but because it assumes everyone processes caffeine at the same speed. They do not.
Half-life isn't the same for everyone
Caffeine has a half-life, the time it takes your body to clear half of it, of roughly 5 to 6 hours on average. But that average hides a lot of variation. Genetics, age, liver function, pregnancy, smoking status, and even other medications can stretch that half-life significantly.
For some people, caffeine from a 2pm coffee is still meaningfully present in their system at midnight. The full breakdown of what moves that number is in how long caffeine actually stays in your system.
What that means for your sleep
Caffeine does not make you feel tired-but-can't-sleep the way stress or a racing mind does. It works quietly, blocking the signal your brain uses to build up sleep pressure over the day.
You might not feel wired. You might just find yourself lying there, tired but not sleepy, without ever connecting it back to the coffee from eight hours earlier.
2pm is not based on your body. It is a rough average built for someone else.
A flat cutoff time is a guess
If you are a slow metabolizer, 2pm is not conservative enough. If you are a fast one, you might be needlessly giving up a 3pm coffee that would have cleared in plenty of time. Either way you are working from a number that was never about you.
Finding your actual cutoff
The only way to know your real cutoff is to work backward from your own clearance rate rather than a generic rule. That is what Caffeinly does. It models your personal caffeine clearance and gives you a sleep-safe cutoff time based on your body, not an average stranger's.
If sleep problems persist even after caffeine stops being a factor, that is worth taking to a doctor rather than an app. Insomnia has plenty of causes, and caffeine is only one of them.