Cola before bed: 33 mg of caffeine and how long it lasts
Updated October 5, 2026 · Sources: U.S. Department of Agriculture · U.S. Department of Agriculture · U.S. Department of Agriculture · U.S. Food and Drug Administration
Short answer
33 mg
per 12 fl oz (355 ml) can
2 h
until under 25 mg is left
One can is a small dose. The 33 mg drops below 25 mg in about 2 hours, so the can itself is rarely the problem. The refill is: a 32 fl oz fountain cup holds nearly 90 mg and needs about 9 hours.
General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.
At 33 mg a single can sits well under a cup of coffee, and the sugar and fizz may bother your evening more than the caffeine does. The risk is volume. Three cans across an evening add up to about 100 mg, and the clock runs from the last sip, not the first.
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.
Because the dose is small, the line falls under the 25 mg planning mark almost at once: 33 mg becomes about 29 mg after one hour and about 25 mg after two. Stack a second can an hour later and the total on the chart is the sum of two separate curves, so the last can sets the finish-by time. The model assumes a 5 hour half-life, which the FDA describes as roughly 4 to 6 hours for most adults. Your own number may differ.
01Last cola 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 | 6:55 pm | 14 mg | 22 mg |
| 9:30 pm | 7:25 pm | 14 mg | 22 mg |
| 10:00 pm | 7:55 pm | 14 mg | 22 mg |
| 10:30 pm | 8:25 pm | 14 mg | 22 mg |
| 11:00 pm | 8:55 pm | 14 mg | 22 mg |
| 11:30 pm | 9:25 pm | 14 mg | 22 mg |
| 12:00 am | 9:55 pm | 14 mg | 22 mg |
| 12:30 am | 10:25 pm | 14 mg | 22 mg |
| 1:00 am | 10:55 pm | 14 mg | 22 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.
02Can, bottle, fountain cup: the same cola at four sizes
Cola is the drink where size, not brand, moves the number. USDA measured regular cola at 9.0 mg per 100 g, with a measured range of 9 to 10 across 6 data points. Multiply by the gram weight USDA lists for each container and the dose climbs from about 33 mg in a 12 fl oz can to about 89 mg in a 32 fl oz cup.
Diet versions run higher. USDA's cola sweetened with aspartame averages 12.0 mg per 100 g, a third more than regular, though its measured range is wide (3 to 20 mg per 100 g across 7 data points). A 12 fl oz diet can works out near 43 mg. Caffeine-free cola is listed at 0.0 mg, which is why the label matters more than the color.
The FDA puts caffeinated soft drinks at 23 to 83 mg per 12 fl oz, so the 33 mg on this page is a low-to-middle value for the can, not a ceiling. A 2-liter bottle poured over an evening of TV is the case people forget: 16 fl oz from it is about 44 mg, and the whole bottle would be close to 190 mg.
| Serving or brew | Caffeine | Basis | Source |
|---|---|---|---|
| 12 fl oz can, regular cola | 33 (33–37) | 9.0 mg per 100 g, range 9–10, 6 data points; multiplied by the USDA can weight of 370 g | USDA FDC 174852 |
| 16 fl oz bottle, regular cola | 44 (44–49) | Same figures multiplied by the USDA weight of 492 g | USDA FDC 174852 |
| 22 fl oz medium fountain cup, regular | 61 (61–68) | Same figures multiplied by the USDA weight of 676 g | USDA FDC 174852 |
| 32 fl oz large fountain cup, regular | 89 (89–98) | Same figures multiplied by the USDA weight of 984 g | USDA FDC 174852 |
| 1 liter of a 2-liter bottle, regular | 93 (93–104) | Calculated by DozeClock: 33.8 fl oz at the USDA 30.7 g per fl oz is about 1,038 g, times 9.0 mg per 100 g | USDA FDC 174852 |
| 12 fl oz can, diet cola with aspartame | 43 (11–71) | 12.0 mg per 100 g, range 3–20, 7 data points; multiplied by the USDA can weight of 355 g | USDA FDC 175099 |
| 16 fl oz bottle, diet cola with aspartame | 57 (14–95) | Same figures multiplied by the USDA bottle weight of 473 g | USDA FDC 175099 |
| 12 fl oz, caffeinated soft drink | 23–83 | FDA consumer update, per 12 fl oz serving | FDA |
| Cola without caffeine | 0 | USDA lists 0.0 mg per 100 g | USDA FDC 174851 |
Per-container values are calculated by DozeClock from USDA mg per 100 g and the USDA gram weight of each container; the 1 liter row also uses a unit conversion. They are not label values for any brand, and USDA does not name brands in these entries.
03Cola next to the three nearest drinks
| Drink | Serving | mg | Hours to under 25 mg | Finish by for an 11 pm bed |
|---|---|---|---|---|
| Black tea | 8 fl oz (237 ml) | 47 | 4 h 33 min | 6:25 pm |
| Cola | 12 fl oz (355 ml) can | 33 | 2 h | 8:55 pm |
| Green tea | 8 fl oz (237 ml) | 28 | 0 h 49 min | 10:10 pm |
| Dark chocolate | 1 oz (28 g) | 24 | 0 h | any time |
mg per serving, not per ounce: servings differ in size · nearest = smallest difference in mg per serving (data/caffeine.json)
Cola has about 2.8 mg per fluid ounce, a quarter of the roughly 12 mg in brewed coffee. That gap closes quickly with size: a 32 fl oz cup of regular cola lands near 89 mg, close to one 8 fl oz cup of brewed coffee. Compare what ends up in your glass, then count the glasses.
Sources
- FoodData Central: Beverages, carbonated, cola, regular (SR Legacy, FDC ID 174852) — U.S. Department of Agriculture
- FoodData Central: Beverages, carbonated, low calorie, cola or pepper-type, with aspartame, contains caffeine (SR Legacy, FDC ID 175099) — U.S. Department of Agriculture
- FoodData Central: Beverages, carbonated, cola, without caffeine (SR Legacy, FDC ID 174851) — 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.