Caffeine Limit Calculator
Your safe daily caffeine ceiling and how many coffees or energy drinks that is.
Enter your values
Enter the body weight in kg.
Enter the coffees today in cups.
Enter the caffeine per cup in mg.
Enter the hours until bedtime in hours.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Safe daily limit
- 400 mg
- Consumed so far
- 285 mg (71% of limit)
- Headroom left
- 115 mg (1.2 more cups)
- Performance dose
- 225 - 450 mg, 45-60 min before
- Still active at bedtime
- 94 mg
- Sleep-safe cut-off
- 12.6 hours before bed
Working
- 1limit = min(400, 6 x 75) = 400 mg
- 2half-life 5 h: 285 x 0.5^(8/5) = 94 mg left
Quick answer
Healthy adults tolerate about 400 mg of caffeine a day, or roughly 6 mg per kg. Performance dosing is 3 to 6 mg/kg taken 45 to 60 minutes before effort.
limit mg = min(400, 6 x kg)
At a glance
| What it does | Your safe daily caffeine ceiling and how many coffees or energy drinks that is. |
|---|---|
| Category | Health |
| Inputs needed | Body weight, Coffees today, Caffeine per cup, Hours until bedtime |
| Main output | Safe daily limit |
| Formula | limit mg = min(400, 6 x kg) |
| Cost | Free — no sign-up, no download |
How to use the Caffeine Limit Calculator
- 1Enter your weight, then how much caffeine you have already had today.
- 2Set hours until bedtime to see what will still be circulating when you try to sleep.
- 3Keep the pre-bed residue under about 50 mg for undisturbed sleep.
Inputs explained
- Body weight(kg)
- Enter the body weight in kg.
- Coffees today(cups)
- Enter the coffees today in cups.
- Caffeine per cup(mg)
- Enter the caffeine per cup in mg.
- Hours until bedtime(hours)
- Enter the hours until bedtime in hours.
Worked example
Using the values the calculator loads with:
Inputs
- Body weight75 kg
- Coffees today3 cups
- Caffeine per cup95 mg
- Hours until bedtime8 hours
Results
- Safe daily limit400 mg
- Consumed so far285 mg (71% of limit)
- Headroom left115 mg (1.2 more cups)
- Performance dose225 - 450 mg, 45-60 min before
- Still active at bedtime94 mg
- Sleep-safe cut-off12.6 hours before bed
- limit = min(400, 6 x 75) = 400 mg
- half-life 5 h: 285 x 0.5^(8/5) = 94 mg left
Frequently asked questions
Is 400 mg safe for everyone?
No. Pregnancy guidance is 200 mg, and people with heart conditions, anxiety or on certain medicines should ask a doctor for a lower ceiling.
How long does caffeine stay in your system?
The half-life averages five hours, so a quarter of a 3 pm coffee is still active at 1 am for many people.
What do I need to enter into the Caffeine Limit Calculator?
Just 4 values: body weight, coffees today, caffeine per cup, hours until bedtime. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Caffeine Limit Calculator work out the answer?
Healthy adults tolerate about 400 mg of caffeine a day, or roughly 6 mg per kg. Performance dosing is 3 to 6 mg/kg taken 45 to 60 minutes before effort. It applies the formula limit mg = min(400, 6 x kg) and shows the working so you can check each step by hand.
Is the Caffeine Limit Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.