Caffeine is the most-used stimulant in the world, and most of us never count it. A flat white, a mid-afternoon tea and a can of cola feel like three different things, but your body sees the same molecule three times. This guide shows what typical drinks contain, what European food-safety experts consider a sensible ceiling, and gives you a small builder to add up your own day.

The numbers that matter

The European Food Safety Authority (EFSA) reviewed the evidence in 2015. For healthy adults it found no safety concern for up to 400 mg of caffeine a day, and none for a single dose of up to 200 mg. For pregnant and breastfeeding women it put the sensible limit at 200 mg a day. Those are population guides, not targets: plenty of people feel jittery well below 400 mg, and some sleep badly after a single afternoon coffee.

That 200 mg single dose is roughly two and a half espressos or two cups of filter coffee drunk close together. Spreading the same coffee across the day is gentler than stacking it.

How much is in a cup?

There is no single figure for "a coffee". Caffeine depends on the bean (robusta carries roughly twice as much as arabica), the dose, the brew method and, above all, the size of the cup. The values below are typical servings from the EUFIC reference table; a café cup is often bigger than the serving listed, and a strong brew can be well above it. Treat them as a sensible estimate, not a lab result.

• Espresso (60 ml): about 80 mg. A small cup, but concentrated.
• Filter coffee (200 ml): about 90 mg. A large mug can be two servings.
• Black tea (250 ml): about 55 mg, depending on leaf and steep time.
• Green tea (250 ml): about 38 mg.
• Cola (355 ml can): about 37 mg.
• Energy drink (250 ml): about 80 mg, often with added sugar and other stimulants.
• Decaf (200 ml): a few milligrams. "Decaffeinated" is low, not zero.

Build your day

Tap the plus and minus buttons to add the drinks you have in a normal day. The bar fills towards your limit. Switch to the pregnancy and breastfeeding limit if that applies to you, and use the cut-off clock to see roughly how much caffeine is still on board when you go to bed.

Why timing matters as much as the total

Caffeine leaves the body slowly. A commonly quoted average half-life is around five hours, which means that if you drink 200 mg at 15:00, about 100 mg is still circulating at 20:00 and about 50 mg at 01:00. Some people clear it faster, others much slower, and pregnancy, some medicines and the contraceptive pill can all slow it down. EFSA notes that even around 100 mg close to bedtime can disturb sleep in some people.

The cheapest way to cut caffeine is not to give up the drink you love, but to move the last one earlier.

When to break the rule of thumb

The 400 mg guide is for healthy adults. It is not a goal to reach. If you get palpitations, a shaky feeling, anxiety or poor sleep, you are your own evidence and the right number is lower. If you are pregnant, breastfeeding, have a heart condition or take medicines that interact with caffeine, ask your doctor or midwife rather than relying on a general guide. And do not mix energy drinks with alcohol: caffeine can mask how drunk you feel, which is a reason to take more care, never a reason to drink more.

Easy ways to lower the total

You do not have to quit. Swap the afternoon cup for decaf or a herbal tea, ask for a single shot instead of a double, pick green tea or black tea over a second coffee, and watch cup size, because a large takeaway can hold two servings. A mocktail or a sparkling water with citrus is a good evening drink that carries no caffeine at all.