Sleep better. Use caffeine smarter.
Three quick calculators answer the questions that actually keep you up: how much caffeine you can have, how much is still in you at bedtime, and when to go to sleep.
Pick what you need right now
Daily caffeine intake
Your safe daily caffeine limit, personalised to your weight — shown in milligrams, cups of coffee and grams of ground coffee.
Calculate my limit → ⏳Caffeine half-life
How much caffeine is still in your system at bedtime — and the latest you can have that afternoon coffee.
Check my bedtime mg → 🌙Sleep cycle
The best times to fall asleep or wake up, timed to 90-minute cycles so you wake up less groggy.
Find my bedtime →Go deeper
Plain-English, science-backed reads to go with the calculators.
Built on the research, not vibes
Caffeine has a half-life of about 5 hours, so an afternoon coffee is still working at midnight. Sleep runs in 90-minute cycles, and waking mid-cycle is what leaves you foggy. And the FDA puts the safe ceiling at about 400 mg of caffeine a day for healthy adults.
Each calculator turns one of those facts into a number you can act on tonight — no accounts, no fluff, no selling your data.
Quick answers
- ~400 mg/day — safe caffeine ceiling for most healthy adults
- ~95 mg — caffeine in one 8 oz cup of coffee
- ~15 g — ground coffee per cup (1:16 ratio)
- 5 h — typical caffeine half-life
- 90 min — length of one sleep cycle
- 8 h before bed — sensible caffeine cutoff
Common questions
How much caffeine can I have a day?
Most healthy adults can have up to 400 mg/day — about four 8 oz coffees. The intake calculator personalises this to your weight and shows it in cups and grams.
How much caffeine is in a cup of coffee?
An 8 oz brewed coffee has roughly 95 mg, an espresso shot ~63 mg, black tea ~47 mg and a cola ~34 mg. Strength and brand vary widely.
Are these calculators free?
Completely. No signup, no email, no paywall — just open one and use it.