Your pillow has no data yet.
Coffee has a
long goodbye.
Plot your drinks. Meet the caffeine that stays for bedtime.
A little less guesswork.
A little more shut-eye.Estimates, not a sleep prediction.
A little more shut-eye.Estimates, not a sleep prediction.
YOUR CAFFEINE, OVER TIME
The long goodbye
0mg remaining
at 14:00
at 14:00
A clean slate.
The kettle is optional.
The kettle is optional.
No drinks yet. No imaginary coffee.
Your half-life3–7h comparisonYour target
Drag the time slider to inspect the curve. Shading compares 3h and 7h half-lives; it is not a confidence interval.
All drinks from 00:00 to midnight.
After the last logged drink.
Your drink lineup 0
Your cups go here. Add the real ones, or plan a what-if.
TUNE THE ASSUMPTIONSEvery body runs
Every body runs
its own café.
Five hours is the spreadsheet’s starting point. Try a different half-life to see how much the answer moves.
These are what-if assumptions, not measured metabolism. The extended setting lets you explore much slower clearance.
25 mg is an arbitrary planning marker, not a proven sleep-safe level. Weight adds mg/kg context; it does not change the half-life.
Population references are not an allowance or a personal safety guarantee. This calculator is for adult scenarios.
THE SMALL PRINT, MADE READABLESame coffee.
Same coffee.
Different goodbye.
What changes clearance, what changes how you feel, and what this little model can actually tell you.
remaining = dose × ½hours ÷ half-lifeCalculate each drink, then add them together.
Sources & model notes
Brand figures are manufacturer values; café and tea figures are estimates. Labels and recipes change. Edit any amount to match your actual drink.
What the model includes (and leaves out)
Each dose enters the model instantly at its logged time, matching the spreadsheet. Actual absorption takes time, so peaks here are a mathematical upper approximation at the dose time, not predicted blood levels. Caffeine is tracked in mg, not blood concentration.
One constant half-life applies to every drink. The model includes only your logged doses (up to two days before and one day after the model day); older unlogged caffeine is omitted. Times are relative 24-hour model days, not calendar dates, so daylight-saving changes are not represented. The below-target result is calculated after every logged future dose, even if outside the visible chart. Exponential decay approaches zero without reaching it.
The 3–7h band is a fixed sensitivity comparison, not a personal range. Sleep quality, tolerance, active metabolites, disease and drug interactions are not calculated. No result certifies that it is safe to drink more or predicts when you will sleep.
Your data
Your drink log and settings stay in local storage on this browser and this site address. They are not sent to an application server. Fonts load from Google Fonts. Clearing site data removes the saved scenario. Changing to another domain does not transfer it.