Should I have coffee now?
Yes
We checked. We always check. Still yes.
Below is what it actually does to your sleep.
What it does to your sleep tonight
Caffeine doesn't stop, it fades. Half of it is gone in about 5 hours, so the real question was never whether to have one. It's how much is still in you when you lie down.
About 95 mg each. Drag them on the chart to set the times.
Where the curve comes from
Caffeine clears at a steady percentage rate, which is why the line drops fast at the top and crawls at the bottom. Half of it goes every 4 to 6.5 hours depending on the person, and that is what the three buttons pick between. Genetics, smoking, some medications and pregnancy all move it. This page asks about none of that.
The dashed line near the bottom sits at 33 mg. Gardiner and colleagues (2023) published two separate cut-off recommendations, and under an average half-life both land within 3 mg of each other, right about there. Below it, caffeine is unlikely to be the thing keeping you up.
Each coffee is treated as arriving all at once, though the real peak is 30 to 45 minutes after the first sip. Next to a five-hour half-life that lag is small, and it makes the evening estimate slightly cautious instead of optimistic.
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Track your coffees in Sipping
Log each coffee as you drink it and this same chart uses the real times instead of assumptions. Sipping keeps the rest too: which coffee it was, how you brewed it, and how it tasted.