Caffeine calculator: how long does caffeine stay in your system?

Each drink is absorbed over about 45 minutes, then its caffeine halves every 5 hours. The calculator adds up every drink still working at each moment of the day, the same curve the Tone app draws on its Caffeine page.

The sleep line is 50 mg: below about that, caffeine stops getting in the way of falling asleep for most people. The “last coffee” time is the latest you could have another 8 oz cup (95 mg) and still be under the line by bedtime, counting what’s already in you.

For most adults, about 5 hours to clear half and 20 to 25 hours to clear almost all of it. How long until it stops affecting you depends on how much you had: a 95 mg coffee drops under 50 mg after about 4.6 hours, a 200 mg cold brew after about 10, and 400 mg after about 15.

The half-life varies a lot from person to person, from about 1.5 to 9.5 hours. Smoking shortens it. Pregnancy, hormonal birth control and some medications lengthen it, sometimes doubling it. The Tone app lets you set your own.

For most people, at least 8 hours before bed for a normal cup, and earlier for a big one. In a sleep-lab study, 400 mg of caffeine taken 6 hours before bed still cut total sleep by more than an hour, and the people taking it didn’t notice. If you go to bed at 11 pm, a 2 to 3 pm cut-off for a regular coffee is a good rule of thumb. The calculator works out yours from what you’ve already had.

The FDA puts it at about 400 mg a day for healthy adults, roughly four 8 oz cups of brewed coffee. The European Food Safety Authority says up to 200 mg at once is fine for most adults. If you’re pregnant or breastfeeding, the usual advice is 200 mg a day or less. Energy drinks and large coffee-shop drinks add up fast: a 16 oz cold brew is about half the day’s limit.

• Brewed coffee, 8 fl oz: about 95 mg
• Espresso, 1 shot: about 63 mg
• Latte or cappuccino, 16 fl oz, 2 shots: about 126 mg
• Cold brew, 16 fl oz: about 200 mg
• Black tea, 8 fl oz: about 47 mg
• Green tea, 8 fl oz: about 28 mg
• Matcha, 1 tsp (2 g): about 70 mg
• Red Bull, 8.4 fl oz can: about 80 mg
• Monster Energy, 16 fl oz can: about 160 mg
• Celsius, 12 fl oz can: about 200 mg
• Coca-Cola, 12 fl oz can: about 34 mg
• Diet Coke, 12 fl oz can: about 46 mg

Brewed coffee and tea vary with the beans, leaves and brewing time, so these are typical figures from USDA FoodData Central and the brands’ own labels.

Log your drinks as you have them. In Tone, say “a large iced oat latte” and the caffeine is counted with its calories. The Caffeine page shows how much is in you now, when you’ll be under the sleep line, and your cut-off for the day. Check the rest of your plan with the calorie calculator.