Caffeine Calculator
Add up the caffeine in your drinks, compare it with the recommended daily limit and see how much will still be in your body at bedtime. Example: two 8 oz cups of coffee and one cola come to about 224 mg, well under the 400 mg adult limit.
Show steps
How to use the Caffeine Calculator
- Enter the values in the fields.
- Press Calculate to see the result with the steps shown.
Formula and method
Total caffeine = sum of (drinks x mg per drink). Caffeine remaining = total x 0.5^(hours / 5), using an average half-life of 5 hours.
Caffeine in common drinks
| Drink | Typical caffeine |
|---|---|
| Brewed coffee, 8 oz | 95 mg |
| Espresso, 1 shot | 63 mg |
| Black tea, 8 oz | 47 mg |
| Green tea, 8 oz | 28 mg |
| Cola, 12 oz | 34 mg |
| Energy drink, 8 oz | 80 mg |
| Decaf coffee, 8 oz | 2 to 7 mg |
Recommended limits
| Group | Daily limit |
|---|---|
| Healthy adults | 400 mg (FDA) |
| Pregnant women | 200 mg (ACOG) |
| Teens | Under 100 mg (AAP) |
| Children | Avoid caffeine |
Caffeine and sleep
Even caffeine taken 6 hours before bed can cut sleep time by about an hour. Stop caffeine by early afternoon if sleep is a problem.
Withdrawal
Cutting down suddenly can cause headaches and tiredness for a few days; reduce gradually. This calculator gives estimates for education and planning, not medical advice. Check with your doctor before major changes to diet, exercise or medicines, especially if you have a medical condition.
Frequently asked questions
How much caffeine is safe per day?
Up to 400 mg for most healthy adults.
How much caffeine in pregnancy?
Under 200 mg a day.
How long does caffeine last?
Its half-life is about 5 hours.
Is 400 mg about 4 cups of coffee?
Yes, about four 8 oz cups.
Can caffeine cause anxiety?
Yes, in sensitive people.
Does decaf have caffeine?
A small amount.
Sources
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