Caffeine Impact On Sleep Calculator

1. Enter your bedtime. Night-shift bedtimes in the morning work too; drink times are counted back from bedtime.
2. Pick how fast you clear caffeine. Leave it on typical unless you smoke, take the combined birth control pill or are in late pregnancy.
3. Add your first and last caffeine of the day. Choose the closest drink and the time you finished it. Pick None if you had only one.

Caffeine half-life is the time your body takes to clear half of the caffeine you drank. With a half-life of 5 hours, a 111 mg coffee drops to about 56 mg after 5 hours, 28 mg after 10 hours and 14 mg after 15 hours.

Caffeine keeps you alert by blocking adenosine, the chemical that builds up while you are awake and makes you sleepy. While enough caffeine is still active, it can delay sleep and make it lighter, even if you do not feel wired.

Half-life varies a lot from person to person. Smoking speeds clearance up, while the combined birth control pill roughly doubles the half-life and late pregnancy extends it further.

The calculator applies the half-life decay to each drink and adds up what is left at bedtime.

1. Coffee at 8:00 AM, bed at 11:00 PM: 15 hours, or 3 half-lives. 111 x 0.5^3 = 14 mg.
2. Coffee at 3:00 PM: 8 hours, or 1.6 half-lives. 111 x 0.5^1.6 = 37 mg.
3. Total left at bedtime: 14 + 37 = about 50 mg, 23% of the 222 mg you drank.
4. Latest caffeine for an 11:00 PM bedtime: 5:00 PM.

The total for the day is modest, but the energy drink lands only 3 hours before bed, so two thirds of it is still active. Moving it to 4:00 PM would cut what is left by more than half.

Real amounts vary with brand, bean and brewing time. Coffee-shop sizes are often 12 to 20 oz, so one cup can be two or more servings. Check the label for energy drinks and pre-workout products, which can contain much more.

Metabolism

Liver enzymes clear caffeine at different speeds in different people, partly because of genes. Smokers clear it faster.

Medicines And Hormones

The combined pill and some medicines slow clearance. Ask a pharmacist if you are unsure about yours.

Pregnancy

Caffeine is cleared much more slowly in late pregnancy, so the same coffee lasts far longer.

Habit

Regular drinkers feel less of a buzz, but caffeine can still disturb sleep measured in a lab.

A 2013 sleep study gave people 400 mg of caffeine at bedtime, 3 hours before or 6 hours before bed. All three disturbed sleep, and even the dose taken 6 hours before bed reduced sleep by more than 1 hour on an in-home monitor.

The 6-hour rule is a minimum. Larger doses and slower metabolism need an earlier cut-off. The 10-3-2-1-0 sleep rule uses an even stricter 10 hours.

• Afternoon coffee drinkers who want to know whether it reaches bedtime.
• Shift workers timing caffeine around daytime sleep.
• People with trouble falling asleep; if it happens most nights, check the pattern with the insomnia severity calculator.
• Pregnant people and pill users, whose caffeine lasts much longer.

Forgetting Hidden Caffeine

Tea, cola, chocolate, pre-workout drinks and some painkillers all add up.

Counting Cups, Not Size

A large coffee-shop coffee can hold two or three standard servings.

Judging By Feel

Not feeling alert does not mean caffeine is not affecting your sleep.

Using Caffeine To Cover Short Sleep

Late caffeine shortens the next night, which drives more caffeine the next day. Good evening habits from sleep hygiene 101 help break the cycle.

The half-life maths is standard, but your real half-life and drink content are unknown, so treat the result as an estimate.

To see whether cutting caffeine helps, compare your nights before and after with the sleep duration calculator.

Stop at least 6 hours before bed. A sleep study found that caffeine taken 6 hours before bed still cut sleep by more than 1 hour.

For many adults it is about 5 hours, but it varies widely. Smokers clear caffeine faster, and pill users and pregnant people more slowly.

With a 5-hour half-life, about a third remains after 8 hours. A 111 mg coffee leaves about 37 mg.

For an 11 PM bedtime, a 3 PM coffee is 8 hours before bed, which meets the 6-hour minimum. Slow metabolizers may need to stop earlier.

The FDA cites 400 mg a day, about two to three 12 oz cups of coffee, as an amount not generally linked to negative effects for most adults.

Decaf still contains a small amount of caffeine, usually far less than regular coffee, so it rarely matters for sleep.

Caffeine can make sleep lighter and shorter even when you fall asleep easily, so you may wake less refreshed.

Caffeine in the evening tends to reduce deep sleep and make sleep more broken, which is one reason late coffee leaves you tired.

• Drake et al. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed (JCSM, 2013) (6-hour cut-off; more than 1 hour of sleep lost)
• FDA: Spilling the beans, how much caffeine is too much? (400 mg a day for most adults)
• MedlinePlus: Caffeine (peak within an hour, effects last hours)
• Energy drinks and the neurophysiological impact of caffeine (Front Neurosci, 2011) (drink content; half-life with smoking and the pill)
• Caffeine metabolism, genetics and health (review) (half-life 6.0 to 3.5 h in smokers; up to 10.5 h late pregnancy)