Start with the label.
Drink sizes, brewing methods and brands change the amount of caffeine. The presets are starting estimates you can edit.
YOUR DAY. YOUR NIGHT. YOUR RHYTHM.
Love your coffee.
Make room for night.
Your last sip can stay with you. Explore how caffeine declines over time, then see what changes when you move a drink earlier.
Find your rhythm
FROM YOUR LAST SIP
TO LIGHTS OUT
A LITTLE MORE SPACE FOR YOUR EVENING.TO LIGHTS OUT
THE CAFFEINE DECAY CALCULATOR
Small shift. See the difference.
Choose your drink, set your times, and explore the curve.
01
What’s in your cup?
Choose a starting point, then adjust the amount.
Drink sizes and caffeine vary. Use the amount on your label when available. FDA caffeine guide
02
Set your rhythm.
From your last sip to lights out.
Half-life is the time needed for the modeled amount to halve. These are scenarios, not a test of your metabolism.
AT 11:00 PM
26 mg remaining
About 29% of this drink, after 9 h.
One drink. A modeled estimate.Watch it wind down.
5-hour half-lifeCurrent timingEarlier timingDashed gray: 25 mg reference
Same drink. A little earlier.
Current timing26 mg
12:30 PM21 mg
At the same bedtime, using the same dose and half-life.
25 MG PLANNING REFERENCE1:45 PM
9 h 15 min before bedtime models 25 mg or less. Read how this reference works below.
A LITTLE CONTEXT
Half gone. Still hanging around.
Half-life, made simple.
With a five-hour half-life, 100 mg becomes 50 mg after five hours, then 25 mg after ten. Explore faster and slower scenarios to see the difference.
Make one small shift.
Keep your bedtime fixed and move the same drink earlier using the slider. Compare the modeled amount remaining at lights out.
How to read your estimate.
This single-drink model uses exponential decay: amount × ½(hours ÷ half-life). It starts at your finish time and does not model absorption or caffeine from other drinks. A bedtime earlier on the clock means the following day; matching times mean zero elapsed hours.
Five hours is a common adult half-life estimate. Actual clearance varies, including with pregnancy, medications and health conditions. The 3-, 5- and 8-hour settings explore scenarios rather than identifying your personal rate. The 25 mg line is an illustrative planning reference, not a proven sleep-safe threshold. This tool estimates an amount; it does not measure your caffeine level or predict your sleep.
KEEP YOUR EVENING YOURS.
A little ritual for the other half of your day.
Explore Nightspan, or build your wind-down with our sleep basics guide.