Caffeine's Half-Life: The Surprising Truth About Why Caffeine Can Keep You Awake

I recently took a Masterclass on Sleep from a neuroscientist.  It wasn't only what I learned, but how he phrased the half-life of coffee that really shook me:

If you're sensitive to caffeine and you drink a coffee at 9am, that's like getting ready for bed at 9pm and saying: "I'll just drink a quarter-cup of coffee."

Who does that?

Not me, that's for sure.  Sure, some folks aren't sensitive to caffeine and can drink it in the evenings without issue.  But for those with a lower tolerance, drinking caffeine later in the day can really keep you awake.

What I wasn't so aware of: The half life of coffee is 6 hoursThis means that, every 6 hours, the amount of caffeine in your system goes down by half.  After another 6 hours, down by half again, and so-on.

Decaf Coffee in Australia

At one stage I was drinking 2-3 cups of coffee per day (with no breaks), so over time, it really adds up to a lot in your system.

To illustrate using the neuroscientist's quote above, this means that drinking a cup of full-strength coffee at 9am would translate to:

  • 9am: Drink a cup of full-strength coffee.  
  • 3pm: Half the caffeine is now out of your system. 50% left.
  • 9pm: Another half is gone.  25% left.
  • 3am (next day): Another half is gone. 12.5% left.
  • 9am (next day): Another half is gone. 6.25% left.
  • 3pm (next day): Another half is gone. 3.123% left.  Let's consider this 'pretty much gone'.

>> That means that, for a 9am cup of coffee, the caffeine is still in your system until around 3-5pm the following day... and that's assuming you haven't piled another cup of normal-strength coffee on top (I rarely took breaks when I drank full-strength coffee, so it would just continue to pile up). 

That blew my mind, and made me reconsider when and how much I drink coffee. Now I mostly drink decaf coffee so I don't have to worry about it -- and whether it'll affect my sleep.

You can see our range of decaf coffees, available Australia-wide, here:

See Decaf Coffee >