Nutrition
Time to clear a fraction
How long until a chosen fraction of the dose has gone.
The Formula
hours = half life x log(fraction) / log(0.5)
How long until a chosen fraction of the dose has gone.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| hours | Time to clear | hours | Hours until only the fraction remains. |
| fraction | Fraction left | decimal | 0.1 for 90 percent cleared, 0.05 for 95 percent. |
| half life | Half life | hours | About 5 hours in healthy adults. |
What Each Symbol Means
hourshours
Time to clear
Hours until only the fraction remains.
fractiondecimal
Fraction left
0.1 for 90 percent cleared, 0.05 for 95 percent.
half lifehours
Half life
About 5 hours in healthy adults.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate caffeine half life page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Caffeine Half Life, filed under Health. Every number the guide produces comes from substituting into this one line.