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Caffeine Calculator

Count the caffeine in your coffee, tea, cola, energy drinks and chocolate, compare it with the 400 mg daily guideline, and see how caffeine builds up and wears off through the day based on its roughly 5 hour half-life.

Drinks today (number of servings)
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mg

Check the label of pre-workouts, pills or specialty drinks.

Timing and limit
hours

0 = all at once.

hours

About 5 h on average; often 2 to 10 h.

mg
Enter your values to see the result.
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How to use the Caffeine Calculator

  1. Enter how many servings of each drink you have in a day. Decimals work (0.5 for half a can).
  2. Add other caffeine in mg for anything not listed, such as a pre-workout or a large coffee-shop drink.
  3. Set the time of your first drink, how many hours your drinks are spread over and your bedtime.
  4. Pick a daily limit and adjust the half-life if you know you process caffeine faster or slower.
  5. Press Calculate caffeine to see your total, the share of your limit, the level at bedtime and the 24-hour curve.

How the caffeine calculation works

  • Total caffeine = Σ (servings × caffeine per serving)
  • Caffeine left after t hours from one dose = dose × 0.5t ÷ half-life
  • With several drinks, the remaining amounts from every serving are added together.

Example: two 95 mg coffees at 8:00 and 14:00 with a 5 hour half-life. At 22:30 the first cup has 14.5 hours behind it (95 × 0.52.9 ≈ 13 mg) and the second 8.5 hours (95 × 0.51.7 ≈ 29 mg), so about 42 mg is still in your system at bedtime.

Caffeine in common drinks

Drink or foodServingTypical caffeine
Brewed coffee8 oz / 240 ml95 mg (70 – 140)
Espresso1 oz / 30 ml shot63 mg
Instant coffee8 oz / 240 ml62 mg
Decaf coffee8 oz / 240 ml2 – 5 mg
Black tea8 oz / 240 ml47 mg
Green tea8 oz / 240 ml28 mg
Cola12 oz / 355 ml can30 – 40 mg
Energy drink8.4 oz / 250 ml can80 mg
Energy drink16 oz / 473 ml can150 – 300 mg
Dark chocolate (70 – 85%)1 oz / 28 gabout 23 mg

Values are typical averages; brands differ. The FDA guideline of 400 mg a day applies to healthy adults. Children, teens, pregnant people and anyone with a heart condition or on medication should follow advice from their doctor.

Frequently asked questions

How much caffeine is too much in a day?

The U.S. FDA says up to 400 mg a day is not generally associated with negative effects in healthy adults, which is about four 8 oz cups of brewed coffee. During pregnancy, ACOG and many health agencies advise staying under 200 mg a day. Sensitivity varies a lot from person to person.

What is the half-life of caffeine?

In healthy adults the half-life of caffeine is about 5 hours on average, with a typical range of roughly 2 to 10 hours. Smoking shortens it, while pregnancy, some medicines and liver conditions can make it much longer.

How is the caffeine left in my body calculated?

Each serving decays exponentially: amount left = dose × 0.5^(hours ÷ half-life). The calculator spaces your servings evenly over the hours you enter and adds up what remains from each one. It ignores the 30 to 60 minutes caffeine takes to be absorbed, so it is an estimate.

How much caffeine is in a cup of coffee?

An 8 oz (240 ml) cup of brewed coffee has about 95 mg on average, but it can range from roughly 70 to 140 mg depending on the beans and brewing method. A 1 oz espresso shot has about 63 mg, and large coffee-shop drinks can contain 200 to 400 mg.

When should I stop drinking caffeine before bed?

Because of the long half-life, caffeine from an afternoon coffee is still partly active at night. A study by Drake and colleagues found that 400 mg taken 6 hours before bed still reduced sleep, so many sleep experts suggest a cutoff of 6 to 8 hours before bedtime.

Are the caffeine values exact?

No. The calculator uses typical values from sources such as the USDA food database. Real products vary, so check the label of energy drinks and specialty coffees and enter the amount in the Other caffeine field for a better estimate. This tool is informational and is not medical advice.

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