Find Your Last Coffee Before Bed
Add up your daily caffeine and estimate when to stop.
This tool was built by Serge (MSc) using established science and government sources. My academic background covers plant biology, environmental biology, and biogeochemistry. My tools are for educational purposes and give practical guidance, not professional advice.
A caffeine cutoff calculator answers two questions: how much caffeine you took in today, and how much will still be in your body at bedtime.
Both answers are estimates, because people clear caffeine at very different speeds.
Step 1: Add up your day
Step 2: Find your bedtime cutoff
Where the numbers come from
The FDA has cited 400 mg a day as an amount not generally associated with negative effects for most adults. Its table of typical amounts runs from about 37 mg in a cup of green tea to 246 mg in a strong energy drink, which is why the tool lets you choose where in each range your drink falls.
Caffeine leaves the body gradually. Its average half-life in healthy adults is about 5 hours, but studies report a range from 1.5 to 9.5 hours.
A rule of thumb you can check by hand
Each half-life cuts the amount in half. A 200 mg coffee leaves about 100 mg after 5 hours, 50 mg after 10, and 25 mg after 15.
That is why a big dose adds less waiting than you would expect. Doubling the dose adds one half-life, not twice the time.
Why your cutoff may not match mine
Genes, pregnancy, smoking, and some medicines change how fast the body clears caffeine. The faster and slower options above show how much the answer can move.
The amounts you pick for how much to leave at bedtime are examples, not medical thresholds. If you sleep lightly, choose the lowest one and see how you feel.
Caffeine you may not see
Pre-workouts and energy products often list caffeine inside a blend without a separate amount. The Proprietary Blend Estimator shows the most an ingredient could be in a blend.
If you also use melatonin in the evening, the Melatonin Timing Calculator helps you plan when to take it relative to bedtime.
Sources
Daily amount and typical drink values: FDA, Spilling the Beans: How Much Caffeine Is Too Much?
Half-life range: Pharmacology of Caffeine, National Academies, hosted by the National Library of Medicine
This tool is for general education only and is not medical or professional advice. Always check product labels and speak with a qualified professional before making decisions about supplements.