How much caffeine is left after 6, 8, 10 or 12 hours?

The short answer

Using a five-hour half-life, about 43.5% of a starting dose remains after six hours, 33.0% after eight hours, 25.0% after ten hours and 18.9% after twelve hours. That means 200 mg becomes about 87 mg, 66 mg, 50 mg and 38 mg at those points.

These are mathematical estimates rather than measured blood levels. A faster three-hour scenario leaves less; a slower seven-hour scenario leaves more. The amount you feel is also not a reliable measure of the amount that remains.

• After 6 hours with a five-hour half-life: about 43.5% remains.
• After 8 hours: about 33.0% remains.
• After 10 hours: 25.0% remains.
• After 12 hours: about 18.9% remains.

How much remains after six hours?

Six hours is slightly longer than one five-hour half-life, so more than one third of the starting dose remains in the central example. A 50 mg dose leaves about 22 mg, 100 mg leaves about 44 mg, 200 mg leaves about 87 mg and 300 mg leaves about 131 mg.

The half-life assumption makes a large difference. Six hours represents two complete three-hour half-lives, leaving 25% of the dose. With a seven-hour half-life, the same six hours leaves about 55.2%. Use this range to see uncertainty rather than selecting the most reassuring column.

How much remains after eight hours?

At eight hours, the five-hour model leaves about one third of the starting dose: roughly 17 mg from 50 mg, 33 mg from 100 mg, 66 mg from 200 mg and 99 mg from 300 mg. This is why an afternoon drink can still contribute meaningful residual caffeine near bedtime.

Timing advice must also account for dose. A smaller 50 mg tea and a 300 mg energy or pre-workout product taken at the same time follow the same percentage decline, but the larger dose leaves six times as many milligrams at every point.

How much remains after ten hours?

Ten hours equals two five-hour half-lives, so the central estimate is exactly one quarter of the starting dose. That gives 12.5 mg from 50 mg, 25 mg from 100 mg, 50 mg from 200 mg and 75 mg from 300 mg.

One quarter remaining does not mean the other three quarters disappeared at once. Exponential clearance is continuous. Ten hours is useful because the arithmetic is simple, but it is not a universal point at which caffeine becomes irrelevant to sleep.

How much remains after twelve hours?

With a five-hour half-life, twelve hours leaves about 18.9% of the starting dose: 9.5 mg from 50 mg, 18.9 mg from 100 mg, 37.9 mg from 200 mg and 56.8 mg from 300 mg. A morning dose can therefore produce a non-zero evening estimate.

With a three-hour half-life, twelve hours represents four halvings and leaves 6.25%. With a seven-hour half-life, about 30.5% remains. Individual clearance varies, so the three-, five- and seven-hour figures are scenarios rather than classifications of “fast”, “normal” or “slow” for a particular reader.

Where the formula comes from

CaffCalc uses the standard exponential half-life relationship: remaining caffeine equals the starting dose multiplied by 0.5 raised to elapsed hours divided by half-life. The same calculation powers the site’s interactive tools, drink timelines and worked tables.

Scientific reviews describe substantial variation in caffeine pharmacokinetics. Genetics, pregnancy, smoking, liver function, hormonal factors and some medicines can affect clearance. That variability is why this guide avoids claiming that one calculated number is a personal measurement.

How to use these estimates responsibly

Use the current label or first-party product information for the starting dose whenever possible, then include every caffeinated item rather than treating earlier drinks as zero. Compare a smaller dose or earlier time using the same assumptions to make the result useful as a planning tool.

The estimates cannot diagnose sleep problems, predict adverse effects or determine a safe personal dose. Seek appropriate medical advice if caffeine is linked to concerning symptoms, pregnancy-specific questions, medicines or an existing health condition.