Caffeine curfew calculator

The half-life is the whole game. Caffeine does not leave in one go, it halves. A 200mg pre-workout at 4pm is still 100mg at 9pm and 50mg at 2am. This page uses five hours, which is the population average, but people genuinely differ: the range runs from about four hours to about nine. If coffee has never once kept you awake you are probably at the fast end and these numbers are pessimistic. If an afternoon flat white reliably costs you sleep, you are at the slow end and the real figures are worse than what you see here.

Why there is no weight box. Caffeine is cleared by an enzyme in the liver, not by body mass, so asking your weight would look scientific and tell you nothing. A 60kg employee and a 95kg one with the same genetics clear it at much the same rate.

Where the 50mg line comes from. Landolt and colleagues measured the sleep EEG directly and found that caffeine suppresses low-frequency delta activity, the slow-wave activity that makes deep sleep restorative, with effects persisting through the night from residual levels as low as 3.5 µmol/L. Drake and colleagues found that 400mg taken six hours before bed cut objectively measured total sleep time by more than an hour. Sleep researchers generally aim for no more than 30 to 50mg still on board at bedtime, which is where this page draws its line. The 20mg figure below it is the point where the effect becomes hard to detect at all.

Your people will probably not feel it. This is the part that matters for a workforce. The disruption shows up on an EEG whether or not anyone notices it, so falling asleep easily after an evening coffee is not evidence it did no harm. Someone losing deep sleep every night will not report a problem, will not take a sick day, and will still be slower and shorter tempered by Thursday afternoon.

Landolt HP, Dijk DJ, Gaus SE, Borbély AA (1995). Caffeine reduces low-frequency delta activity in the human sleep EEG. Neuropsychopharmacology 12(3), 229 to 238.
Drake C, Roehrs T, Shambroom J, Roth T (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine 9(11), 1195 to 1200.

Why this matters at work. Poor sleep is one of the quietest drains on a working day. It shows up as slower decisions, shorter patience and an afternoon that takes more effort than it should, none of which appear on a sickness record. Caffeine timing is one of the few levers that costs nothing to pull.

Why Combat Fuel are at the top of the supplement list. Wayfinder co-founder Tom Collins uses their products and has a commercial arrangement with them, which is why they head that group rather than sitting in alphabetical order. Their figures are worked out exactly the same way as every other product here, and in their case that meant listing both pre-workouts lower than the number on the tub: the headline counts di-caffeine malate at its full weight and, on one product, 200mg of TeaCrine, which is a stimulant but is not caffeine and does not behave like it.

Averages, not diagnosis. Individual clearance varies a lot, and pregnancy, the combined pill and some medications slow it considerably. If sleep is a real problem for you, that is a conversation with a GP, not a calculator.