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Energy drink before bed: 72 mg of caffeine and how long it lasts
Updated October 5, 2026 · Sources: Red Bull · U.S. Department of Agriculture · U.S. Food and Drug Administration
Short answer
72 mg
per 8 fl oz (237 ml)
7 h 38 min
until under 25 mg is left
Read the can size before the number. At 72 mg it takes about 7 h 40 min to fall under 25 mg, but the same drink in a 20 fl oz can carries almost three times that and needs close to 15 hours.
General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.
Model: remaining = dose × 0.5^(hours ÷ 5). Half-life 5 h (Institute of Medicine 2001); real half-lives run 1.5–9.5 h between people.
A 72 mg drink halves every 5 hours: about 36 mg at hour 5, 18 mg at hour 10. The line crosses 25 mg between the two, which is where the 7 h 40 min comes from. Energy drinks often arrive with sugar and are sipped slowly, so the dose is spread over 30 to 60 minutes rather than swallowed at once, and the curve here starts at the last sip. The 5 hour half-life is an average; the FDA says 4 to 6 hours for most adults.
01Last energy drink by bedtime
| Bedtime | Finish by (25 mg left) | Left at lights out if finished 6 h before | Left if finished 3 h before |
|---|---|---|---|
| 9:00 pm | 1:20 pm | 31 mg | 48 mg |
| 9:30 pm | 1:50 pm | 31 mg | 48 mg |
| 10:00 pm | 2:20 pm | 31 mg | 48 mg |
| 10:30 pm | 2:50 pm | 31 mg | 48 mg |
| 11:00 pm | 3:20 pm | 31 mg | 48 mg |
| 11:30 pm | 3:50 pm | 31 mg | 48 mg |
| 12:00 am | 4:20 pm | 31 mg | 48 mg |
| 12:30 am | 4:50 pm | 31 mg | 48 mg |
| 1:00 am | 5:20 pm | 31 mg | 48 mg |
Finish-by times are rounded down to 5 minutes. 25 mg is this site's planning line, not a clinical threshold. Every drink at once: caffeine cutoff grid.
02One category, a 6-fold spread: what the can size does
The FDA lists energy drinks at 41 to 246 mg of caffeine per 12 fl oz. That is a six-fold gap inside one product type. The 72 mg used on this page for 8 fl oz sits in the lower half of that range.
The one brand page fetched for this article shows the other lever, which is size. Red Bull states 80 mg for an 8.4 fl oz can, 114 mg for 12, 151 mg for 16 and 198 mg for 20. Per fluid ounce the strength barely moves, at about 9.5 mg. So the can you reach for changes the dose far more than the flavor does.
USDA's own entry for a Red Bull-style drink measures 29 mg per 100 g, which is slightly lower than the label: about 75 mg for the 8.4 fl oz can. Both figures are real, one from a lab sample and one from the maker. Use the larger one when you plan around sleep. Two small cans back to back are 160 mg, 40% of the FDA's 400 mg daily figure for healthy adults.
| Serving or brew | Caffeine | Basis | Source |
|---|---|---|---|
| 8.4 fl oz can, Red Bull (label) | 80 | Stated on the brand page: "One 8.4 fl oz can of Red Bull Energy Drink contains 80 mg of caffeine" | Red Bull Q&A |
| 12 fl oz can, Red Bull (label) | 114 | Stated on the same brand page | Red Bull Q&A |
| 16 fl oz can, Red Bull (label) | 151 | Stated on the same brand page | Red Bull Q&A |
| 20 fl oz can, Red Bull (label) | 198 | Stated on the same brand page | Red Bull Q&A |
| 8.4 fl oz can, USDA lab data | 75 (75–77) | 29.0 mg per 100 g, range 29–30, 3 data points; multiplied by the USDA can weight of 258 g | USDA FDC 173210 |
| 12 fl oz, USDA lab data | 107 (107–111) | Same figures multiplied by the USDA weight of 369 g | USDA FDC 173210 |
| 16 fl oz, USDA lab data | 143 (143–148) | Same figures multiplied by the USDA weight of 492 g | USDA FDC 173210 |
| 12 fl oz, energy drink (any brand) | 41–246 | FDA consumer update, per 12 fl oz serving | FDA |
Per-size USDA values are calculated by DozeClock from mg per 100 g and the USDA gram weight of each portion. The Red Bull rows are the maker's figures for one product line; other brands differ, and this page does not publish figures for brands whose pages were not fetched.
03Energy drink next to the three nearest drinks
| Drink | Serving | mg | Hours to under 25 mg | Finish by for an 11 pm bed |
|---|---|---|---|---|
| Energy drink | 8 fl oz (237 ml) | 72 | 7 h 38 min | 3:20 pm |
| Matcha (1 tsp powder) | 8 fl oz (237 ml) | 70 | 7 h 26 min | 3:30 pm |
| Espresso | 1 fl oz (30 ml) shot | 64 | 6 h 47 min | 4:10 pm |
| Instant coffee | 8 fl oz (237 ml) | 62 | 6 h 33 min | 4:25 pm |
mg per serving, not per ounce: servings differ in size · nearest = smallest difference in mg per serving (data/caffeine.json)
At roughly 9 mg per fluid ounce, an energy drink is about three-quarters of brewed coffee by volume, yet the cans are bigger than a coffee cup, so the totals meet in the middle. A 16 fl oz can at 151 mg is more than one 8 fl oz cup of coffee at 96 mg. The comparison table counts one serving each; drink two and double the row, then add the extra hours to your finish-by time.
Sources
- How much caffeine is in a can of Red Bull Energy Drink? — Red Bull (official U.S. site)
- FoodData Central: Beverages, Energy drink, RED BULL (SR Legacy, FDC ID 173210) — U.S. Department of Agriculture
- Spilling the Beans: How Much Caffeine is Too Much? — U.S. Food and Drug Administration
General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.