Free tool
Caffeine Calculator
See how much caffeine stays in your body over time and how much is still in your system when you go to bed. Adjust the dose, the time you drank it, and your bedtime.
Espresso ~80 mg, brewed coffee ~120 mg, energy drink ~150 mg, Aftershock 160 mg.
Average is 5 hours. Smokers ~4 h. Pregnancy and some medications stretch it to 8+ h.
Caffeine in your system at 23:00
53 mg
8 h after your 160 mg dose
Mild sleep impact possible
Around 50 to 100 mg can lengthen the time it takes to fall asleep and lighten deep sleep for sensitive people.
Caffeine over time
How it works
Your body clears caffeine through first-order elimination: a fixed fraction leaves every hour. The half-life is how long it takes for half the dose to clear, about 5 hours for a typical healthy adult. After one half-life you have 50% left, after two roughly 25%, after three about 12%.
That is why an afternoon coffee can still be working at midnight. The calculator uses your dose, the time you took it, and the half-life to estimate how much is left when you go to bed.
Energy without the late-night payback
Aftershock is dosed at 160 mg of caffeine for focus and paired with L-theanine for calm, smooth energy. No jitters, no tingling. Train earlier in the day and the curve above stays low by bedtime.
See AftershockWant the full breakdown? Read our guide to caffeine before training.
Frequently asked questions
How long does caffeine stay in your body?
Caffeine has an average half-life of about 5 hours, so half is gone after 5 hours and a quarter after 10. A 160 mg dose still leaves roughly 40 mg in your system 10 hours later. Smoking shortens the half-life, while pregnancy and some medications can stretch it past 8 hours.
How many hours before bed should I stop caffeine?
A common guideline is to stop caffeine at least 6 to 8 hours before bed. Use the calculator to see how much is still circulating at your planned bedtime and adjust your last dose to keep it under about 50 mg.
Is 160 mg of caffeine a lot?
No. 160 mg is a moderate dose, similar to a strong cup of coffee, and well within the 400 mg per day that health authorities consider safe for most healthy adults. Aftershock is dosed at 160 mg and paired with L-theanine for focus without the jitters.
Does the calculator account for body weight or tolerance?
It models the standard 5 hour half-life, which is the strongest driver of how much caffeine is left at bedtime. Tolerance changes how the same dose feels, but clearance speed is mostly set by genetics, smoking, pregnancy and medications. Adjust the half-life field if any of those apply to you.
This calculator is an educational estimate based on average caffeine pharmacokinetics. It is not medical advice. Individual clearance varies with genetics, liver function, pregnancy, medication and other factors.