UNDERSTAND THE METHOD
How to use this calculator
Add each drink or food, its caffeine amount, serving count, and time. Edit preset amounts to match the label. The chart covers one calendar day. For bedtime after midnight, the calculator uses the following day when needed.
What the result can tell you
This is a simplified absorption and elimination model, not a blood concentration test. Half-life varies with medicines, health, pregnancy, and other factors. The FDA adult reference of 400 mg/day and the European Food Safety Authority (EFSA) pregnancy reference of 200 mg/day are comparison values. They are not a target or a guarantee of safety. This adult tool is not for children.
Common questions
How does the bedtime caffeine result work?
Add each drink or food, its caffeine amount, serving count, and time. The calculator applies the selected half-life assumption across one calendar day and sums the modelled remainder at bedtime.
Are the 400 mg and 200 mg comparison amounts safety limits?
No. They are comparison values in a simplified model, not targets or guarantees of safety. This adult tool is not for children.
Sources & limitations4 sources
Sources checked September 12, 2026 for the earlier method references. FDA and EFSA references checked October 5, 2026. These notes identify methods and assumptions. They have not received an independent clinical review.
- FDA context for caffeine amounts and individual sensitivity.fda.gov
- European Food Safety Authority (EFSA) reference for the 200 mg/day pregnancy comparison.efsa.europa.eu
- Review of individual variation in caffeine metabolism.pubmed.ncbi.nlm.nih.gov
- Study of caffeine timing and sleep.pubmed.ncbi.nlm.nih.gov