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Caffeine Cutoff Calculator

How much caffeine is still in you at bedtime — and when is your last call for coffee?

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Caffeine still in your body at 11:00 PM

63mg

There's still a fair amount of caffeine in you at bedtime. Get ready to count a lot of sheep.

Target 50 mgBed25006:00 AM12:00 AM (next day)
  • Last call for a 150 mg cup3:05 PM
  • Total today300 mg
  • FDA 400 mg reference400 mg

You're already past your bedtime target today — no more caffeine. The single-cup deadline assumes it's your only cup today.

Today's caffeine

First cup

8:30 AM
mg

FDA: 12 oz brewed coffee 113–247 mg, 12 oz black tea about 71 mg, 12 oz soda 23–83 mg, 12 oz energy drink 41–246 mg. Enter 0 if you skip it.

Second cup

2:00 PM
mg

Third cup

5:00 PM
mg

Sleep and your body

11:00 PM
hrs

About 5 hours on average for healthy adults, ranging roughly 1.5–9.5 hours. Raise it if caffeine lingers for you.

mg

Lower is more cautious — lower it if caffeine affects you strongly

mg

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That afternoon coffee is still with you at midnight

Caffeine doesn't disappear when you stop feeling it. With an average half-life of 5 hours, a 150 mg coffee at 8:30 AM and another at 2:00 PM still leave about 63 mg in your body at 11:00 PM.

Flip it around: to fall asleep at 11:00 PM with less than 50 mg on board, if it's your only cup today, finish a 150 mg coffee by 3:05 PM. A big 250 mg cup moves the deadline up to 11:23 AM; an 80 mg small one can wait until 7:37 PM. If you already had coffee this morning, the deadline comes even earlier — the calculator handles that for you.

How it's calculated

  • Caffeine left from a cup at time t = mg × 0.5 ^ (hours elapsed ÷ half-life)
  • Caffeine at bedtime = the sum of what's left from every cup
  • Single-cup deadline = bedtime − half-life × log₂(cup mg ÷ target)
  • One-more-cup deadline = bedtime − half-life × log₂(cup mg ÷ (target − what's left from today's cups))

The model assumes caffeine is absorbed instantly and cleared at a constant rate. In reality it starts working about 15 to 30 minutes after you drink it (EFSA), so treat the result as an estimate. Cups scheduled after bedtime aren't counted.

What the research says

In a 2013 study in the Journal of Clinical Sleep Medicine, people took 400 mg of caffeine 0, 3, or 6 hours before bed. Even the 6-hour group had noticeably disrupted sleep. The European Food Safety Authority also notes that 100 mg close to bedtime can affect sleep in some adults.

Sleep well and still drink coffee

  • Front-load your caffeine. The same cup in the morning leaves far less at bedtime than one in the afternoon.
  • Go smaller after lunch. Halve the caffeine and your deadline moves back by one half-life.
  • Count tea, soda, and energy drinks. They all contain caffeine, too.
  • Watch your daily total. The FDA has cited 400 mg a day as an amount not generally linked to negative effects for most healthy adults.

FAQ

What is caffeine half-life?

It is the time it takes your body to clear half the caffeine. In healthy adults it averages about 5 hours but ranges widely, roughly 1.5 to 9.5 hours. If caffeine keeps you up, try a longer half-life.

How much caffeine is too much?

The FDA has cited 400 milligrams a day — roughly two to three 12-ounce cups of brewed coffee — as an amount not generally associated with negative effects for healthy adults. Sensitivity varies, and pregnancy and some medications change the picture.

How much caffeine is in my drink?

According to the FDA, 12 ounces of brewed coffee has about 113–247 mg, 12 ounces of black tea about 71 mg, and 12 ounces of soda about 23–83 mg. Check the label or the chain’s nutrition info for exact numbers.

Is this medical advice?

No. It is a simplified model that assumes instant absorption and a constant half-life. If you have trouble sleeping or health concerns, talk to a doctor.

Sources and updates

Last updated:

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