What the model does
The calculator uses an exponential half-life model:
Remaining caffeine = dose × 0.5(hours elapsed ÷ half-life)
The default half-life is five hours. You can change it between three and seven hours to see how a different assumption changes the estimate. This is not a measurement of your individual metabolism.
Why half-life varies
Caffeine half-life differs between people and can be influenced by genetics, pregnancy, medication, smoking, liver function and other factors. A single default number cannot capture that variation.
What the 50 mg target means
“Target remaining at bedtime” is a planning threshold chosen for this tool. It is not a medical safety limit and it does not guarantee that you will or will not sleep. Change the target if you prefer a different planning assumption.
How to use the result
- Enter the amount from a product label when possible; serving sizes vary widely.
- Enter the time you finished the caffeinated drink.
- Set your planned bedtime and a target amount.
- Use the cutoff as a planning prompt, not a guarantee.
Related reading
See how sleep cycles work, or use the nap calculator when you need a short sleep window.