Caffeine half-life · Evidence-led guide
Two coffees vs one large coffee: how doses add up over time
The short answer
Equal daily totals can produce different later estimates when the timing differs. Decay each dose from its own intake time before adding the amounts.
| Schedule | At 4 pm | At 10 pm |
|---|---|---|
| 200 mg at 8 am | 66.0 mg | 28.7 mg |
| 100 mg at 8 am + 100 mg at noon | 90.4 mg | 39.4 mg |
The doses are illustrative, not measured coffee recipes. Remaining = sum of each dose × 0.5^(its elapsed hours ÷ 5). No sleep or safety threshold is implied.
Why the split schedule differs
The second dose has had four fewer hours to decline. Treating the whole day’s caffeine as if it were consumed at breakfast would understate the later contribution. The correct model computes each intake independently and sums the results.
Real coffee still needs a source
The example deliberately uses equal hypothetical totals to isolate timing. Two real small coffees may not equal one real large coffee. Look up the serving amounts first, then enter the actual times into the calculator.
Test assumptions rather than predict sleep
Change the half-life to see how sensitive the result is to the assumption. A precise-looking decimal is still model output. It cannot establish your metabolism, measured blood concentration or whether you will sleep well.
Sources and scope
- Nehlig (2018): differences in caffeine metabolismBackground on variability; the illustrative five-hour assumption is not a personal measurement.
Educational information, not medical advice. Published, calculated and approximate values have different limits. Check the current product label or recipe when an exact amount matters.