There's a widely agreed number for healthy adults, and both US and European regulators land on it.
The 400 mg rule
Both the FDA and the European Food Safety Authority (EFSA) consider up to 400 mg of caffeine per day safe for most healthy, non-pregnant adults — roughly four cups of coffee.
Pregnancy is different
ACOG, EFSA and the NHS all recommend no more than 200 mg per day in pregnancy. Caffeine is cleared much more slowly then — its half-life can rise to ~15 hours in the third trimester, so it accumulates.
- Jitteriness, a racing heart, or anxiety
- Trouble falling or staying asleep
- Headaches, or an afternoon crash you “need” more caffeine to fix
Caffy sets a personal daily limit and shows a live gauge, so you can see when you're approaching 400 mg — before, not after.