How This Caffeine Calculator Works
This tool does two things. First, it calculates your personalised safe daily caffeine limit based on your body weight, age, and sensitivity. Second, it lets you tap the drinks you have consumed so you can track your running total against that limit in real time.
The safe limit is based on the pharmacological standard used by researchers and health authorities: approximately 6 milligrams of caffeine per kilogram of body weight for healthy adults, capped at the FDA and EFSA recommended maximum of 400mg per day. If you select the pregnancy option, the limit drops to 200mg in line with guidance from the American College of Obstetricians and Gynecologists. Teenagers and sensitive individuals receive a reduced limit as well.
How Much Caffeine Is in Common Drinks?
Caffeine content varies by bean, brand, brewing method, and serving size, but these are reliable average values used by this calculator:
| Drink | Serving | Caffeine |
|---|---|---|
| Brewed coffee | 240ml (8oz) | 95mg |
| Espresso shot | 30ml (1oz) | 63mg |
| Instant coffee | 240ml (8oz) | 62mg |
| Cold brew | 240ml (8oz) | 155mg |
| Latte / Cappuccino | 1 shot base | 63mg |
| Black tea | 240ml (8oz) | 47mg |
| Green tea | 240ml (8oz) | 28mg |
| Red Bull | 8.4oz can | 80mg |
| Monster Energy | 16oz can | 160mg |
| Cola (Coke/Pepsi) | 355ml can | 34mg |
| Dark chocolate | 1oz (28g) | 24mg |
| Decaf coffee | 240ml (8oz) | 3mg |
What Is a Safe Daily Caffeine Limit?
For healthy adults, the FDA and the European Food Safety Authority both consider up to 400mg of caffeine per day to be safe - roughly four to five cups of brewed coffee. This calculator personalises that figure using your body weight, since a 90kg adult can safely process more caffeine than a 50kg adult.
Certain groups need lower limits. Pregnant women should stay under 200mg per day. Teenagers should generally stay under 100mg. People who are sensitive to caffeine, take certain medications such as some antidepressants or oral contraceptives, or have heart conditions may need to consume far less. The calculator adjusts for weight, age, and pregnancy, but it cannot account for medication interactions, so always consult your doctor if you are unsure.
How Long Does Caffeine Stay in Your System?
Caffeine has a half-life of roughly 5 to 6 hours in a typical adult. This means that if you drink a coffee containing 95mg of caffeine at 3pm, about 47mg is still active in your body at around 8pm, and roughly 24mg at 1am. This is why an afternoon coffee can disrupt sleep even if you do not feel wired at bedtime.
Individual clearance rates vary widely. Smokers metabolise caffeine faster, while pregnancy, oral contraceptives, and some medications slow it down significantly. If caffeine affects your sleep, a useful rule of thumb is to stop consuming it 8 to 10 hours before bed.
Signs You Have Had Too Much Caffeine
Exceeding your personal caffeine limit can cause jitters, anxiety, a racing heart, headaches, digestive discomfort, and insomnia. These effects usually appear well below dangerous levels and are simply your body signalling that you have had more than it is comfortable with. If you regularly experience these symptoms, try reducing your intake gradually rather than stopping suddenly, as abrupt withdrawal can cause headaches and fatigue.