Caffeine Intake Calculator

How much caffeine is too much?

For most healthy adults, the FDA points to 400 mg of caffeine per day as an amount not generally associated with negative effects. That is roughly four 8 oz cups of brewed coffee, two energy shots, or about ten cans of cola. It is a ceiling, not a target, and plenty of people feel better well below it.

Two extra guardrails are worth knowing. First, keep single servings under about 200 mg at one time, since large one-shot doses are where jitters, a racing heart, and stomach upset tend to show up. Second, body size matters: a common reference is roughly 5.7 mg of caffeine per kg of body weight per day, so a smaller person hits their personal ceiling sooner. Enter your weight above and the calculator uses the lower of 400 mg or your body-weight ceiling. If you regularly pass your limit and feel wired or anxious, the simplest fix is to trim a serving or two rather than push through.

Caffeine in common drinks

The calculator's presets use typical average values so you can sanity-check your total. Real content swings with brand, cup size, and brew strength, so treat these as ballpark figures.

• Brewed coffee: about 95 mg per 8 oz cup
• Espresso: about 64 mg per shot
• Cold brew: about 155 mg per 8 oz
• Instant coffee: about 62 mg per 8 oz
• Decaf coffee: about 3 mg per 8 oz (not caffeine-free)
• Black tea: about 47 mg per 8 oz
• Green tea: about 28 mg per 8 oz
• Matcha: about 70 mg per 1 tsp serving
• Energy drink: about 80 mg per 8.4 oz can
• Large energy drink: about 160 mg per 16 oz
• Energy shot: about 200 mg per 2 oz
• Cola / soda: about 34 mg per 12 oz can
• Pre-workout: about 200 mg per scoop
• Caffeine pill: about 100 mg per tablet

Notice how fast the high-dose options stack up. A single pre-workout scoop or energy shot is already half the adult daily limit, and a 16 oz energy drink plus a couple of coffees can clear 400 mg before lunch.

Caffeine and sleep: when to stop drinking it

Caffeine has an average half-life of about 5 hours in healthy adults. So if you drink a 200 mg coffee at 3 p.m., roughly 100 mg is still circulating at 8 p.m. and about 50 mg at 1 a.m. That lingering stimulant can cut your total sleep time and your deep sleep even if you fall asleep fine.

Research has found that 200 mg of caffeine taken six hours before bed can measurably reduce sleep. That is why a common rule of thumb is to stop caffeine about 6 to 8 hours before lights out, aiming to get residual levels below roughly 25 to 50 mg. Add your last-caffeine time and your bedtime above, and the calculator estimates how much is left at bedtime plus a recommended last-cup time based on the half-life decay. If you are sensitive, push that cutoff even earlier.

Tracking caffeine during a 75-day challenge

Caffeine sits right where three things a 75-day challenge cares about meet: hydration, sleep, and discipline. Coffee and energy drinks have a mild diuretic effect, so heavy intake can quietly work against your daily water goal. A late afternoon cup can shave the deep sleep you need to recover from two workouts. And an energy shot before a session can spike your heart rate higher than you planned.

The fix is not to quit, just to keep an eye on the total and the timing. Set a personal daily cap and a hard cutoff time, then check yourself against them each day. If you want a free way to make that a repeatable habit alongside your water and workout streaks, you can log a caffeine-cutoff or hydration task in Reset75 and watch the streak build day after day. Pair this with the water intake calculator to balance the diuretic effect, and the heart rate zone calculator if pre-workout is part of your routine.