Caffeine Remaining
Caffeine’s half-life averages five hours. An americano at 3 pm (about 150 mg) still leaves close to half in your system at 11 pm.
Your numbers
Remaining
49.5mg
Percentage
33%
What it means
49.5 mg remains after 8 hours.
Formula
Remaining = Caffeine (mg) × 0.5 ^ (Hours later ÷ Time to clear)
Half-life ranges from 2 to 10 hours between people; pregnancy, oral contraceptives and liver disease all lengthen it.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Caffeine (mg)Caffeine taken in; a single Americano runs about 120 mg. | 150 | 10 ~ 1,000 |
| Hours laterHow long it has been since you drank it. | 8 | 0 ~ 48 |
| Time to clear (h)Hours until the alcohol clears; it varies a lot by person. | 5 | 1 ~ 12 |
Step by step
Quick reference table
Results when only Caffeine (mg) changes and everything else stays put.
| Caffeine (mg) | Remaining (mg) | Percentage (%) |
|---|---|---|
| 75 | 24.7 | 33 |
| 113 | 37.3 | 33 |
| 150 | 49.5 | 33 |
| 225 | 74.2 | 33 |
| 300 | 99 | 33 |
What each result means
| Result | At default values |
|---|---|
| Remaining (mg)How much is still in you; it halves about every five hours. | 49.5 |
| Percentage (%)A share expressed out of 100. | 33 |
Common mistakes
Half-life ranges from 2 to 10 hours between people; pregnancy, oral contraceptives and liver disease all lengthen it.
Glossary
- Caffeine (mg)
- Caffeine taken in; a single Americano runs about 120 mg.
- Hours later
- How long it has been since you drank it.
- Time to clear
- Hours until the alcohol clears; it varies a lot by person.
- Remaining
- How much is still in you; it halves about every five hours.
- Percentage
- A share expressed out of 100.
Frequently asked questions
Q. How is Caffeine Remaining calculated?
Remaining = Caffeine (mg) × 0.5 ^ (Hours later ÷ Time to clear) — Caffeine’s half-life averages five hours. An americano at 3 pm (about 150 mg) still leaves close to half in your system at 11 pm.
Q. Can you walk through an example?
With Caffeine (mg) 150, Hours later 8, Time to clear 5h, the answer is Remaining 49.5mg.
Q. What do I need to enter?
Enter Caffeine (mg), Hours later, Time to clear. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Caffeine (mg) moves the answer to Caffeine (mg) 75 → Remaining (mg) 24.7 and Caffeine (mg) 300 → Remaining (mg) 99. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Half-life ranges from 2 to 10 hours between people; pregnancy, oral contraceptives and liver disease all lengthen it.
Related calculators
These calculators help you understand health figures; they do not replace diagnosis or prescription. See a clinician if you have symptoms.