How long does caffeine last? Coffee, caffeine and your sleep

That 3pm flat white feels like a good idea at the time. Then it's 11pm and your brain is still wide awake. So how long does caffeine last, and how late is too late?

Here is what happens after your coffee, how much caffeine is in common drinks, a sensible daily amount, and how the Thrive Health Band and the Thrive by Optihealth app can show you what your own coffee habit does to your nights.

How long does caffeine last?

Caffeine is absorbed quickly. You usually start to feel it within about 30 minutes, and levels in your blood peak somewhere between 30 and 70 minutes after your drink.

The noticeable lift tends to last around three to seven hours, depending on the person. But that's not the whole story. Caffeine leaves your body gradually, and the Sleep Health Foundation notes it can take up to 24 hours to clear completely.

A useful way to think about it is half-life: the time it takes your body to clear half of the caffeine you had. For healthy adults it is often quoted at around five hours, though it varies a lot from person to person. So if you have a strong coffee at 3pm, a good share of that caffeine can still be in your system at 8pm, and some of it at bedtime.

Why it varies so much from person to person

Two people can drink the same coffee and have very different nights. Things that can change how long caffeine lasts for you include:

Your genes. Some bodies clear caffeine quickly, others slowly.
Age. Caffeine tends to stay active for longer as we get older.
Pregnancy and some contraceptive pills. Both can slow how quickly caffeine is cleared.
Smoking. Nicotine speeds it up.

How much caffeine is in coffee?

It depends on the drink, the bean and who made it, but healthdirect gives these rough figures:

Espresso (50 mL cup): about 145 mg
Instant coffee (1 teaspoon): about 80 mg
Energy drink (250 mL can): about 80 mg
Black tea (220 mL cup): about 50 mg
Cola (375 mL can): about 36 mg

A double-shot cafe latte can sit well above an instant coffee at home, so "two coffees" can mean very different amounts.

How much caffeine is too much?

Healthdirect says healthy adults can generally have around 400 mg of caffeine a day. That's roughly two espressos or four instant coffees. If you are pregnant or breastfeeding, the guide is 200 mg a day, and your GP or midwife can talk it through with you.

Regular heavy use, above about 600 mg a day, is linked with trouble sleeping, heartburn and feeling anxious. Caffeine can also interact with some medicines, so ask your pharmacist if you're not sure about yours.

For sleep, timing matters as much as the daily total.

How caffeine affects your sleep

Caffeine blocks a chemical in the brain that builds up during the day and makes you feel sleepy. Handy at 10am, less so at 10pm. Close to bedtime, it can:

make it harder to fall asleep
make your sleep lighter, with more waking through the night
shorten your total sleep, even if you don't notice it

That last point is the sneaky one. In one well-known study, caffeine taken six hours before bed still cut total sleep by more than an hour.

When to stop drinking coffee before bed

There's no single cut-off that suits everyone. The Sleep Health Foundation suggests avoiding caffeine for at least three to seven hours before sleep, and earlier still, such as after lunch, if you're sensitive or already sleeping poorly.

A few simple ways to try it:

Pick a cut-off time. 2pm is a common starting point if you go to bed around 10pm.
Count every source. Tea, cola, energy drinks, pre-workout and chocolate all add up.
Swap, don't just stop. Decaf, herbal tea or a short walk can fill the afternoon slot.
Cut down gradually. Dropping caffeine suddenly can bring headaches and tiredness for a few days, so try one less drink a day.
Give it a week. One night tells you very little. Compare a week or two.

See what caffeine does to your own sleep with Thrive

General advice only goes so far, because your body clears caffeine at its own pace.

Wear the Thrive Health Band day and night and open the Thrive by Optihealth app in the morning. Sleep detail shows how long you slept, a chart of your stages through the night, and your deep, light and awake time, with week and month views to compare. Overnight the Band also tracks resting heart rate, HRV and temperature. It has no screen, so it's comfortable in bed, and up to 14 days of battery means fewer nights lost to charging.

In your Daily Check-In you can tag Coffee or Energy drinks. Over time, Thrive learns what is usual for you right across your health, from sleep, heart and activity to mood, energy, stress, meals, medications and more. So rather than comparing you with an average, it can show whether your nights look different on days you had caffeine later.

Want to test it properly? In Insights, the 7-day Caffeine cut-off experiment asks you to have no caffeine after 2pm, then compares your sleep duration, sleep efficiency, stress and HRV with your own baseline from before you started. Check in each day, and at the end you'll see what moved. As the app puts it, it's a signal, not a verdict.

You can also ask Ask Thrive things like:

"Do I sleep less on days I tag coffee after lunch?"
"Is my HRV lower after days with energy drinks?"
"How did my sleep change during my caffeine experiment?"

Your Today's Vitality score includes a Sleep and Recovery driver. And if you'd like someone else to see your sleep, Thrive Loops lets you share selected information with a participating trainer, health professional or someone you trust. You decide what to share and with whom, and you can change or revoke access at any time.

When to talk to your GP

If you feel you can't get through the day without a lot of caffeine, or you're tired most days even with enough time in bed, it's worth booking in with your GP. Thrive isn't a diagnosis, but your sleep trends, check-in history and medications are all in the app, and Ask Thrive can help you pull together what has changed and when before your appointment.

Before you buy

You'll need a compatible iPhone or Android phone, because the Thrive app is on the Apple App Store and Google Play, in Australia and eight other countries. The app stores are only for downloading the app, though; they aren't where you buy the Band or a Plan. You can buy at thrivehealthband.com, or at a participating World Gym Australia location or health and wellness clinic.

The Thrive Health Band is A$660 for the first year under the launch offer. That includes the Band, which is yours to keep, and 12 months of the Thrive by Optihealth app, My Health on the web, Health Fingerprint, Ask Thrive, Thrive Loops and your data, paid once upfront. Prices are in AUD and include GST. Free Australia-wide shipping during the launch offer (usually A$14.99).

Nothing renews automatically. After your first year, you can get a new band plus 12 more months for A$660, or keep your band and renew the Thrive Connected Plan for A$240 a year, or A$29 a month with no lock-in.

You're also covered by a 12-month Thrive Care Warranty, and consumer guarantees under Australian Consumer Law always apply. See Returns if something is wrong with your purchase.

Common questions

Does decaf have caffeine?

A little, but only a small fraction of regular coffee, so it's a handy afternoon swap.

Why can I drink coffee at night and still fall asleep?

Falling asleep isn't the same as sleeping well. Caffeine can still make sleep lighter or shorter, so look at your sleep data over a week, not just how quickly you nodded off.

Is tea better than coffee in the afternoon?

Black tea usually has less caffeine than coffee, and herbal teas have none.

For more answers, see Questions.