How long does 300 mg of caffeine last?
About 17 hours. 300 mg of caffeine peaks near 274 mg 45 minutes after you take it, halves every 5.7 hours, and falls below the 40 mg sleep threshold about 17 hours later.
| Peak level, 45 minutes in | 274 mg |
| Time to fall below 40 mg | 17 hours |
| Left after 6 hours | 148 mg |
| Left after 12 hours | 71 mg |
| Latest hour for an 11 pm bedtime | 6:14 am |
| Share of the 400 mg daily limit | 75% |
Hour by hour
| Time after the dose | If taken at 8 am | Still active | For sleep |
|---|---|---|---|
| 1 hour | 9 am | 270 mg | still working |
| 2 hours | 10 am | 241 mg | still working |
| 4 hours | 12 pm | 189 mg | still working |
| 6 hours | 2 pm | 148 mg | still working |
| 8 hours | 4 pm | 116 mg | still working |
| 10 hours | 6 pm | 91 mg | still working |
| 12 hours | 8 pm | 71 mg | still working |
| 16 hours | 12 am | 44 mg | still working |
| 24 hours | 8 am | 17 mg | clear |
What 300 mg looks like
300 mg is three mugs of filter coffee, a full serving of many pre-workouts, or a Celsius followed by a coffee. As a day's total it is moderate. As a single dose it is half as much again as the European Food Safety Authority considers safe to take at once.
It needs about 17 hours to fall under 40 mg. Count back from your bedtime and the arithmetic is blunt: for an 11 pm night the last moment for 300 mg is 6:14 am. After that hour some of it is still active when you lie down.
| Drink | One serving | To reach 300 mg |
|---|---|---|
| Filter coffee | 96 mg per 8 oz cup | 3.1 |
| Espresso | 64 mg per 1 oz shot | 4.7 |
| Black tea | 48 mg per 8 oz cup | 6.2 |
| Red Bull | 80 mg per 8.4 oz can | 3.8 |
| Coca-Cola | 32 mg per 11.2 oz can | 9.4 |
How late can you take it?
Count back 17 hours from the time you go to bed. Each bedtime below has its own page with the cutoff for every drink.
| Bedtime | Latest hour for 300 mg |
|---|---|
| 9 pm | 4:14 am the night before |
| 9:30 pm | 4:44 am the night before |
| 10 pm | 5:14 am |
| 10:30 pm | 5:44 am |
| 11 pm | 6:14 am |
| 11:30 pm | 6:44 am |
| midnight | 7:14 am |
| 1 am | 8:14 am |
If you clear caffeine faster or slower
Half-life runs from about four hours in fast metabolisers to eight or more in slow ones, and the difference compounds over a day.
| Metabolism | Half-life | Clears in | Latest for 11 pm |
|---|---|---|---|
| Fast | 4.1 hours | 12 hours | 10:51 am |
| Average | 5.7 hours | 17 hours | 6:14 am |
| Slow | 7.9 hours | 23 hours | the day before |
Common questions
How long does 300 mg of caffeine last?
About 17 hours for an average adult. 300 mg peaks near 274 mg active 45 minutes after you take it, then halves every 5.7 hours until it falls below 40 mg, the line Cira uses as low enough to sleep on.
Is 300 mg of caffeine a lot?
As a single dose, yes. 300 mg is above the 200 mg that the European Food Safety Authority considers safe to take at once. As a day's total it is within the 400 mg limit for a healthy adult.
How late can I take 300 mg of caffeine and still sleep?
For an 11 pm bedtime the latest is 6:14 am. Move it by the same amount as your own bedtime. People who clear caffeine slowly need about 23 hours, so they should stop earlier still.
How much of a 300 mg dose is left after 12 hours?
About 71 mg, for an average adult. After 6 hours about 148 mg is still active, and after 24 hours about 17 mg.
Other doses
Look it up another way
Where these numbers come from
Every figure is calculated with the model the Cira app uses: caffeine peaks 45 minutes after you take it and halves every 5.7 hours, a typical value for healthy adults. The 40 mg sleep line is a working threshold of the model, and the 400 mg daily limit is the figure used by the European Food Safety Authority and the US FDA. These are averages. Smoking, pregnancy, the contraceptive pill and some medicines change how fast you clear caffeine. How the numbers are worked out.
