Find your safe daily caffeine limit and what it equals in drinks.
Updated Sep 2026Fill in the fields and press Calculate. Every range comes from the sources listed under the tool.
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Sources
- Spilling the Beans: How Much Caffeine is Too Much? FDA
- Caffeine EFSA
- How much coffee can I drink while I'm pregnant? ACOG
- Caffeine - StatPearls - NCBI Bookshelf NIH (NCBI Bookshelf)
How Much Caffeine Is Safe Per Day?
This caffeine calculator works out a personal daily limit from your body weight. For healthy adults, the FDA and the European Food Safety Authority put the safe ceiling at about 400 mg of caffeine a day, roughly four cups of brewed coffee, with no more than about 200 mg in a single sitting. Because caffeine is dosed by body weight (around 5.7 mg per kg per day), smaller people hit their limit sooner, which is what this calculator accounts for.
Pregnancy changes the math: guidance from ACOG and EFSA caps intake at 200 mg a day, because caffeine crosses the placenta and is cleared much more slowly during pregnancy. This tool is for adults; the limits for teenagers are lower and are a question for their doctor. People who feel jittery on small amounts are often slow metabolisers, a genuine genetic difference in the CYP1A2 enzyme that clears caffeine, and do better at half the standard limit.
The Timing Rule That Matters Most
Caffeine has a half-life of about five hours, so half of your 4 pm coffee is still circulating at 9 pm, and a quarter at 2 am. It does not just delay sleep; it cuts deep sleep even when you fall asleep fine. The practical rule: last caffeine at least 8 hours before bed. If you sleep at 11 pm, that means nothing after 3 pm. Our sleep calculator pairs naturally with this one, and the page on what is a normal blood pressure explains what caffeine does to a reading.
Signs You Are Over Your Limit
- Jitters, racing heart, or anxiety in the hours after drinking
- Needing caffeine to avoid a headache (dependence, not energy)
- Waking at 3 am wired despite being exhausted
- An afternoon crash that sends you back for more
Frequently Asked Questions
Is coffee bad for you?
At normal doses, the research runs the other way: moderate coffee drinking is associated with lower risk of type 2 diabetes, liver disease, and Parkinson’s. The problems come from dose, timing, and what gets added to the cup.
How long does caffeine stay in your system?
Half is gone in about 5 hours, but full clearance takes over a day. Genetics swing this widely: fast metabolizers clear it in half the time of slow ones, which is why the same latte treats two people so differently.
Does caffeine dehydrate you?
Not at normal intakes. The mild diuretic effect is smaller than the fluid the drink provides, so coffee and tea count toward your daily fluids. Our water calculator includes them.
How do I cut back without headaches?
Taper instead of quitting cold. Drop by half a cup every few days, or swap one coffee for tea. Withdrawal headaches peak around day two of abrupt stops and are mostly avoidable with a one to two week taper.
Sources
- Spilling the Beans: How Much Caffeine is Too Much? · FDA
- Caffeine · EFSA
- How much coffee can I drink while I'm pregnant? · ACOG
- Caffeine – StatPearls – NCBI Bookshelf · NIH (NCBI Bookshelf)
This calculator is for general information only. If you have a heart condition, anxiety disorder, or are pregnant, discuss caffeine with your doctor.