How to Use Caffeine Calculator
The Caffeine Calculator estimates your caffeine intake and how much is still in your body. Pick a drink preset or enter custom mg, set servings, half-life and hours since drinking.
- Pick a drink — Coffee, espresso, latte, energy drink, tea, cola, or custom.
- Enter servings and mg per serving — Adjust if your drink is stronger.
- Set half-life and hours since last cup — Default 5 h half-life for adults.
- Read the result — The Caffeine Calculator shows total mg, % of daily limit, remaining safe limit, and estimated mg still in body.
Formula & Theory — Caffeine Calculator
The Caffeine Calculator uses two equations:
total = mg_per_serving × servings
percent = total ÷ 400 × 100
in_body(t) = total × 0.5^(t ÷ half_life)| Drink | Typical mg per serving |
|---|---|
| Brewed coffee | 95 (240 ml) |
| Espresso | 63 (30 ml) |
| Latte | 75 |
| Energy drink | 80 |
| Black tea | 47 |
| Green tea | 28 |
| Cola | 22 |
Assumptions and Limits
The Caffeine Calculator uses average half-life (3–7 h). Pregnancy, oral contraceptives, smoking, and some medications change the rate. People sensitive to caffeine may feel effects far below 400 mg.
Use Cases for Caffeine Calculator
The Caffeine Calculator is useful for:
- Sleep planning — Estimate residual caffeine before bedtime.
- Daily limit tracking — Stay under the 400 mg FDA guideline.
- Comparing drinks — Quickly see how one energy drink stacks against two coffees.
- Caffeine sensitivity — Find the threshold where you feel jittery.
Use the Caffeine Calculator before your afternoon coffee to protect your sleep — and before your morning ritual to know what you’re really drinking.