How much caffeine is in Diet Mountain Dew?
A 12 fl oz can of Diet Mountain Dew has 54 mg of caffeine.
That's about half a cup of brewed coffee, and 14% of the 400 mg a day the FDA cites for most healthy adults.
Source: Center for Science in the Public Interest · checked 10 Nov 2026
When did you have it?
Had at 3 pm, about 19 mg is still in you at an 11 pm bedtime. That should not affect most people’s sleep.
Your whole day, every drink, in the free CaffeineIQ check. The iPhone app is coming soon.
Latest time to drink it
For an 11 pm bedtime, a 12 fl oz can of Diet Mountain Dew stays under the 50 mg most people sleep fine with, even late in the evening. The table works it out for other bedtimes and for how sensitive you are: it is the latest time to start one so that the caffeine left stays under the line all night.
| Bedtime | Very sensitive under 25 mg | Average under 50 mg | Not very sensitive under 100 mg |
|---|---|---|---|
| 9 pm | 2:55 pm | Any time | Any time |
| 10 pm | 3:55 pm | Any time | Any time |
| 11 pm | 4:55 pm | Any time | Any time |
| Midnight | 5:55 pm | Any time | Any time |
| 1 am | 6:55 pm | Any time | Any time |
For a 12 fl oz can of Diet Mountain Dew, average clearance (half-life 5 h), 8 hours of sleep. "Any time" means even one at bedtime stays under the line.
How long it lasts
The caffeine from a 12 fl oz can of Diet Mountain Dew peaks in your blood about 75 minutes after you start it, at roughly 46 mg. Half of it is gone in about 5 hours for an average adult; that ranges from roughly 3 to 7 hours, and longer in pregnancy or with some medicines.
| Time after | 3 hours | 6 hours | 9 hours | 12 hours |
|---|---|---|---|---|
| Still in you | 38 mg | 25 mg | 17 mg | 11 mg |
So one had at 3 pm leaves about 19 mg at 11 pm. How long caffeine lasts explains the curve.
How it compares
Diet Mountain Dew is stronger than 64% of the 15 sodas we track, by caffeine per serving.
Per fluid ounce (4.5 mg) it is stronger than 64% of them.
To reach 400 mg in a day you would need about 7½ of these.
Less caffeine
- Olipop Vintage Cola 50 mg, 12 fl oz can
- fritz-kola Organic 50 mg, 330 ml bottle
- Diet Coke 46 mg, 12 fl oz can
More caffeine
- Poppi Alpine Blast 55 mg, 12 fl oz can
- Olipop Citrus Rush 60 mg, 12 fl oz can
- Mountain Dew Zero Sugar 68 mg, 12 fl oz can
Same caffeine: Mountain Dew.
FAQ
Is Diet Mountain Dew high in caffeine?
It is moderate. A 12 fl oz can of Diet Mountain Dew has 54 mg, which is 57% of the 95 mg in an 8 fl oz cup of brewed coffee.
Can I drink Diet Mountain Dew at night?
For most people, yes: even late in the evening a 12 fl oz can of Diet Mountain Dew stays under 50 mg at an 11 pm bedtime.
How long does the caffeine in Diet Mountain Dew last?
It peaks about 75 minutes after you start it. Of the 54 mg, about 25 mg is still in you 6 hours later and 11 mg after 12 hours, for an average adult with a 5-hour half-life.
Does Diet Mountain Dew have more caffeine than a cup of coffee?
No. A 12 fl oz can of Diet Mountain Dew has 54 mg; an 8 fl oz cup of coffee has 95 mg.
Method and limits
The caffeine figure comes from Center for Science in the Public Interest; recipes, brewing and batches vary, so a real serving can differ. The curves use a standard one-compartment model with an average 5-hour half-life and a sleep-friendly line of 50 mg; your own body may clear caffeine faster or slower. How it works has the details.
These are estimates for information, not medical advice.