The model
How long does caffeine stay in your body?
Caffeine fades gradually rather than disappearing at a fixed hour. CoffeeCutoff turns that process into a last-coffee time with a simple half-life estimate.
One drink, fading over time
A half-life is the time it takes the estimated caffeine remaining in your body to fall by half. This 120 mg latte example shows the pattern used by the calculator.
Parameters
| Setting | Normal | Sensitive |
|---|---|---|
| Half-life | 5.5 hours | 7 hours |
| Reference point | 50 mg | 50 mg |
Sensitivity changes how quickly the estimate falls, not the shared reference point. Actual caffeine clearance varies from person to person.
Reference point
Why 50 mg?
Research does not define a universal safe amount of caffeine remaining at bedtime. We use 50 mg to turn a continuous decay estimate into one useful time. It is a product reference point, not a medical safety threshold.
Cutoff calculation
remaining = dose × 0.5 ^ (hours / half_life)
The calculator finds the latest drink time that brings the estimate to about 50 mg by bedtime, then rounds the result to a 15-minute time. Check impact runs the same model in the other direction and estimates what is left at bedtime.
Limitations
Drink caffeine amounts are averages, and actual half-life changes with age, pregnancy, medication, smoking, and other factors. Sensitivity to caffeine also differs, so your response may not match the estimate. This is general guidance, not medical advice.