Caffeine and focus
Caffeine takes time to work. Here is when it is likely to peak, so you can line up your hardest work with it.
Your details
100 mg at 14:00
14:30 to 16:00
when caffeine usually peaks in the blood (30 to 120 minutes after)
- Plan your focus work forfrom about 14:30
- Left at your 23:00 bedtime (4 hour half life)21 mg
- Your day so far240 mg of the 400 mg EFSA daily guide
- This drink100 mg
EFSA says caffeine is absorbed with a peak 30 to 120 minutes after you drink it, so a coffee as you sit down helps the second half of a session more than the first. Pregnant? The NHS limit is 200 mg a day. Caffeine cannot replace sleep: if you rely on it to get through every afternoon, your nights may need a look.
See your GP if changing your sleep habits has not helped, you have had trouble sleeping for months, or it is making it hard to cope. If you feel sleepy while driving, stop somewhere safe.
The working
100 mg at 14:00, 140 mg earlier, bed at 23:00
EFSA says caffeine peaks in the blood 30 to 120 minutes after you drink it, so your window is 14:30 to 16:00. Your day total is 240 mg, under the 400 mg guide. With a 4 hour half life, about 21 mg is still there at 23:00, and 14:00 is well clear of the NHS 6 hours before bed.
The EFSA guides
For healthy adults
| Guide | Amount |
|---|---|
| A day | up to 400 mg |
| In one go | up to 200 mg |
| Pregnant | up to 200 mg a day |
| Near bedtime | 100 mg can affect sleep in some adults |
Getting the most from it
Without wrecking your night
- Have it as you sit down, so the peak lands mid session
- Keep your biggest cup earlier in the day
- Pair it with a short break and some daylight when the session ends
- If you need it every afternoon, look at your sleep
Read with care
What this cannot tell you
- Make up for lost sleepCaffeine masks tiredness; it does not repay it.
- Know your sensitivitySome people feel jittery on much less.
- Advise on heart conditionsAsk your GP about caffeine if you have palpitations or a heart condition.
Questions
Common questions
How long does caffeine take to kick in?
EFSA says it is absorbed with a peak in the blood 30 to 120 minutes after drinking.
How much caffeine is safe a day?
For healthy adults, EFSA says up to 400 mg a day, and up to 200 mg in one go. EFSA and the NHS both say up to 200 mg a day in pregnancy.
Does caffeine improve concentration?
It can make you feel more alert, but it does not replace sleep, and too much can make you jittery.
When is too late for coffee?
The NHS says avoid caffeine in the 6 hours before bed.
Sources
- EFSA Scientific Opinion on the safety of caffeine, EFSA Journal 2015 (absorbed with a peak at 30 to 120 minutes; half life about 4 hours)
- EFSA explains: caffeine (400 mg a day, 200 mg single doses, 100 mg near bedtime, half life about 4 hours)
- NHS: insomnia (relax at least 1 hour before bed; no exercise 4 hours before; no caffeine, alcohol or smoking 6 hours before; reviewed 19 March 2024)
Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.
When to see a GP about sleep
See your GP if changing your sleep habits has not helped, you have had trouble sleeping for months, or it is affecting your daily life and making it hard to cope. If you feel sleepy at the wheel, stop somewhere safe.
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