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Night toolkit / 01

Caffeine curve

Caffeine has a half-life of about 5 hours: half of that 15:00 coffee is still working at 20:00, and a quarter near 01:00. Log your day, set your bedtime, and see exactly what is left in your bloodstream when your head hits the pillow. Everything stays in your browser.

1. Log the day's caffeine

  • 07:00Filter coffee, 95 mg
  • 13:30Espresso shot, 63 mg
5 h

Typical is about 5 hours; pregnancy, some medicines and genetics stretch it well beyond.

2. Watch it decay

Milligrams of caffeine still in your system across the day. Hover or touch the chart to read any moment.

50100mg06:0008:0010:0012:0014:0016:0018:0020:0022:0000:00Bedtime 22:30

3. What lands in your night

~29 mg

Still circulating at 22:30

That is about a cup of green tea taken right at bedtime.

158 mg

Total consumed today

FDA reference for healthy adults: up to 400 mg/day. A reference, not a target.

In a controlled trial, caffeine taken even 6 hours before bed measurably cut sleep time (Drake et al, 2013). The curve is an estimate built on your half-life setting: pregnancy, oral contraceptives, liver conditions and some medicines slow caffeine clearance well past the typical 5 hours.

Sources

  1. Spilling the Beans: How Much Caffeine is Too Much? US Food and Drug Administration, 2024400 mg/day reference for healthy adults; half-life 4 to 6 hours.
  2. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed Journal of Clinical Sleep Medicine (Drake C, Roehrs T, Shambroom J, Roth T), 2013
  3. How Long Does Caffeine Keep You Awake? Houston Methodist, 2021Typical half-life about 5 hours; individual range roughly 2 to 10 hours.
  4. FoodData Central: caffeine content of beverages US Department of AgricultureDrink presets are typical estimates; brands and brew strength vary.

Last reviewed: 2026-07-16

Go deeper

Want to see what your nights actually look like? Our pillar site Healthspan publishes plain-language explainers on sleep trackers and smart rings, plus a daily habit coach with its book.

Sleep tracking explainers at healthspan.muNext: plan tonight's sleep window

How the curve works

Caffeine is cleared by the liver in a pattern called first-order elimination: a fixed fraction is removed per hour, so the amount remaining halves over each half-life. For a typical healthy adult that half-life is about 5 hours, but the true range runs from roughly 2 to 10 hours. Pregnancy, oral contraceptives, some antibiotics and liver conditions slow clearance; heavy smoking speeds it up.

The tool treats absorption as immediate, which slightly overstates the early peak: in reality blood levels top out 30 to 60 minutes after drinking. For a bedtime decision that simplification is conservative, which is the right direction for sleep.

Why it matters: in a randomized trial, 400 mg of caffeine taken a full 6 hours before bed still cut measured sleep by about an hour. If the curve shows a meaningful dose landing in your night, moving your last coffee earlier is one of the highest-leverage sleep changes available, and it costs nothing.