How much caffeine is in Diet Coke? A 12 oz can has 46 mg, according to The Coca-Cola Company, while a 12 oz can of regular Coca-Cola or Coke Zero Sugar has 34 mg. So Diet Coke has about a third more caffeine than regular Coke. Both are well under an 8 oz cup of brewed coffee, which has about 95 mg.
That makes soda easy to underestimate. A can with dinner feels harmless, but caffeine has an average half-life of about 5 hours, so some of it is still around at bedtime. The caffeine calculator shows exactly how much for your own drinks and bedtime.
Free toolCaffeine Cutoff CalculatorHow much caffeine is still in you at bedtime, and your latest cup.How much caffeine is in Coke, Diet Coke and Coke Zero?
Coca-Cola lists 34 mg per 12 oz for Coke and Coke Zero Sugar, and 46 mg per 12 oz for Diet Coke. These figures come from the company's own US product and FAQ pages, checked in October 2026.
| Drink | 12 oz can | 20 oz bottle* |
|---|---|---|
| Coca-Cola (Original) | 34 mg | about 57 mg |
| Coca-Cola Zero Sugar | 34 mg | about 57 mg |
| Diet Coke | 46 mg | about 77 mg |
| Cherry Coke, Cherry Coke Zero Sugar | 34 mg | about 57 mg |
| Diet Cherry Coke | 34 mg | about 57 mg |
| Caffeine-Free Coca-Cola, Diet Coke or Coke Zero Sugar | 0 mg | 0 mg |
| For comparison: brewed coffee, 8 oz | about 95 mg |
*The 20 oz numbers are scaled from the 12 oz figures. Coca-Cola doesn't list them separately, so treat them as estimates.
Recipes and labels can change, and amounts can differ outside the US. If the can or the brand's site lists a caffeine number, go with that.
Why does Diet Coke have more caffeine than Coke?
It's simply how Diet Coke is made: Coca-Cola lists 46 mg per can versus 34 mg for Coke. The company doesn't explain the difference, and Coke Zero Sugar doesn't follow Diet Coke: it matches regular Coke at 34 mg.
So "diet" or "zero sugar" on the label says nothing about caffeine. The only versions without it are the ones labeled caffeine-free.
How much caffeine is in other sodas?
Most colas land around 30 to 45 mg per 12 oz can, and many clear or fruit sodas have none. For sodas without a manufacturer figure, USDA FoodData Central gives generic averages:
| Soda type (USDA generic) | Caffeine per 12 oz |
|---|---|
| Regular cola | about 33 mg |
| Pepper-type soda with caffeine | about 37 mg |
| Diet cola or pepper-type with aspartame | about 43 mg (tested samples ranged widely, roughly 11 to 71 mg) |
| Caffeine-free cola | 0 mg |
The diet range is the one to notice. USDA's tested samples varied a lot, so a diet soda can be much stronger than average. Coca-Cola also lists Sprite, Sprite Zero, Fresca and its Fanta flavors as caffeine-free.
For energy drinks, which can carry several times more caffeine than any soda, see energy drinks and sleep. For coffee, tea and soda side by side, see the caffeine in drinks chart.
How much caffeine is left at bedtime from an evening Coke?
A can of Coke at 7 PM leaves about 20 mg in you at 11 PM, and a Diet Coke at the same time leaves about 26 mg. The table uses the site's caffeine math: remaining caffeine = dose x 0.5^(hours / 5).
| Can at | Coke or Coke Zero (34 mg) | Diet Coke (46 mg) | Two cans of Coke (68 mg) |
|---|---|---|---|
| 3 PM | 11 mg | 15 mg | 22 mg |
| 5 PM | 15 mg | 20 mg | 30 mg |
| 7 PM | 20 mg | 26 mg | 39 mg |
| 9 PM | 26 mg | 35 mg | 52 mg |
All values are for an 11 PM bedtime. This site treats about 25 mg at bedtime as a sensible ceiling. It isn't an official limit, but it's a useful line. A Diet Coke with a 7 PM dinner ends up about where a regular Coke at 9 PM does.
Two cans change the picture. Two Cokes together come to 68 mg, and for an 11 PM bedtime they'd need to be finished by about 3:45 PM to drop under 25 mg.
What's the latest time to drink a Coke or Diet Coke?
For an 11 PM bedtime, finish a can of Coke by about 8:45 PM and a can of Diet Coke by about 6:35 PM. In hours, that's roughly 2 hours 15 minutes before bed for Coke and about 4 hours 25 minutes for Diet Coke.
| Bedtime | Coke or Coke Zero, 12 oz | Diet Coke, 12 oz | Coke, 20 oz | Diet Coke, 20 oz |
|---|---|---|---|---|
| 9:00 PM | 6:45 PM | 4:35 PM | 3:05 PM | 12:55 PM |
| 10:00 PM | 7:45 PM | 5:35 PM | 4:05 PM | 1:55 PM |
| 10:30 PM | 8:15 PM | 6:05 PM | 4:35 PM | 2:25 PM |
| 11:00 PM | 8:45 PM | 6:35 PM | 5:05 PM | 2:55 PM |
| Midnight | 9:45 PM | 7:35 PM | 6:05 PM | 3:55 PM |
These are averages. Some people clear caffeine much more slowly, and pregnancy, some medications and liver problems can stretch it out. If an afternoon soda already keeps you up, treat these times as too late. For an hour-by-hour view of the half-life, read how long caffeine lasts.
Can a Diet Coke at night keep you awake?
It can, especially if you're sensitive or it's your second or third can of the day. A single 46 mg can is a small dose next to a coffee, but timing matters more than the size.
Falling asleep fine doesn't mean caffeine had no effect. In an at-home sleep study, a large dose taken 6 hours before bed cut total sleep by more than an hour, and people generally didn't notice. A can of soda is far smaller than that dose, but the direction is the same: caffeine tends to make sleep lighter and shorter.
Easy swaps for the evening:
- Switch to the caffeine-free version after mid-afternoon. Same taste, no caffeine.
- Pick a 12 oz can over a 20 oz bottle. The bottle carries about two thirds more.
- Count every can. Three Diet Cokes come to 138 mg, more than a cup of coffee. If you're tallying a whole day, how much caffeine is too much covers the 400 mg limit the FDA considers generally safe for healthy adults.