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What Time Should You Stop Drinking C4 Energy Before Bed?

Last-call times for C4 Energy computed from its sourced caffeine content and the 5-hour median half-life.

TL;DR

To be under 50 mg of residual caffeine at an 11 PM bedtime, have your last 16 oz can of C4 Energy (200 mg) by 1:00 PM (13:00). The math uses the median 5-hour caffeine half-life; individual half-lives range from about 2 to 12 hours.

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C4 Energy Last-Call Times by Bedtime

Latest time to finish a 16 oz can of C4 Energy (200 mg of caffeine) and still be under 50 mg of residual caffeine at bedtime, assuming the median 5-hour half-life. Your personal half-life may sit anywhere in the 2 to 12 hour range.

BedtimeLast call for C4 EnergyResidual at bedtime
9:00 PM (21:00)11:00 AM (11:00)~50 mg
10:00 PM (22:00)12:00 PM (12:00)~50 mg
11:00 PM (23:00)1:00 PM (13:00)~50 mg
12:00 AM (00:00, midnight)2:00 PM (14:00)~50 mg

Clearance Time by Serving Size

How long each serving of C4 Energy needs before bed to drop under 50 mg:

ServingCaffeineTime needed before bed
16 oz can200 mg10 h

Source: caffeine figures from Caffeine Informer, accessed 2026-06-11. Values can vary by batch, location, and preparation; check the label or the source for the latest figures.

How the Math Works

Caffeine leaves your body by exponential decay. With the median 5-hour half-life, the 200 mg in a 16 oz can of C4 Energy falls to 100 mg after 5 hours and 50 mg after 10 hours. To get under 50 mg, the level where caffeine stops measurably delaying sleep for most people, it needs about 10 h of clearance time. Subtract that from your bedtime and you get the last-call times above, rounded down to the nearest 15 minutes.

The big caveat: the 5-hour figure is a median. Depending on CYP1A2 genetics, medications, smoking, and pregnancy, real half-lives run from about 2 to 12 hours. If caffeine reliably keeps you up, treat these times as too generous and move your personal cutoff earlier, or model your own curve in the caffeine half-life calculator.

Related Guides

Half-Life CalculatorPersonalize the cutoff to your metabolism Caffeine in C4 EnergyEvery serving size, sourced All Sleep CutoffsLast-call times for 100+ drinks Caffeine and SleepThe science of timing your last cup

Frequently Asked Questions

There is no magic number, but around 50 mg of circulating caffeine the alerting effect fades for most people, which makes it a practical sleep-ready marker (the same one the Unbuzz app and our half-life calculator use). For C4 Energy, that means the 200 mg in a 16 oz can needs about 10 h of decay to get under that mark. Caffeine-sensitive sleepers may need to aim lower; the calculator lets you change the threshold.
These times assume the median 5-hour half-life, but CYP1A2 genetics, oral contraceptives, pregnancy, some medications, and age stretch individual half-lives across roughly 2 to 12 hours. At an 8-hour half-life, the 200 mg in a 16 oz can of C4 Energy needs about 16 h to clear instead of 10 h, so a slow metabolizer should stop hours earlier than this table suggests. The caffeine half-life calculator adjusts the curve to your profile.
Residual caffeine adds up. Two servings (400 mg total) need about 15 h to clear under 50 mg, noticeably longer than one. Log each serving in the half-life calculator or the Unbuzz app to see the combined curve.
Standard exponential decay: residual = dose x 0.5^(hours / 5), using the drink's sourced caffeine content (200 mg per 16 oz can, per Caffeine Informer) and the median 5-hour half-life. The last call is the latest time that leaves under 50 mg at bedtime, rounded down to 15 minutes so the rounding never works against your sleep.

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Medical Disclaimer: Caffeine values are approximate figures from the cited public sources. Actual content may vary by batch, location, and preparation, and caffeine metabolism varies widely between individuals. This page is for informational purposes only and is not medical advice. The FDA guideline for healthy adults is up to 400 mg of caffeine per day; the recommended limit during pregnancy is 200 mg per day. Consult a healthcare professional for personalized guidance.