Caffeine Calculator — Content Tracker & Half-Life

Log drinks to track daily caffeine intake vs the FDA's 400 mg benchmark, or find how much caffeine remains in your system via the half-life formula.

July 8, 2026

Drink

Typical range 70–140 mg

Brewed Coffee (8 oz)

95 mg

Black Tea (8 oz)

47 mg

Total Caffeine Logged

142 mg

36% of the FDA's commonly cited 400 mg/day general benchmark for healthy adults

Content Tracker sums the caffeine in every drink you log and compares it against the FDA's commonly cited 400 mg/day general benchmark for healthy adults — individual sensitivity varies, and this is not a medical limit. Half-Life Calculator uses Remaining = Dose × 0.5^(Hours Elapsed ÷ Half-Life). Caffeine's half-life typically runs 1.5–9.5 hours in healthy adults (commonly cited as 5–6 hours), but pregnancy can extend it up to roughly 15 hours by the third trimester and smoking can shorten it by 30–50%. This tool provides general information only, not personalized medical advice — pregnant individuals, those with heart conditions, and anyone with caffeine sensitivity should follow their doctor's specific guidance.

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Reference Values

Last verified: Jul 8, 2026

Category	Range	What It Means	Status
Dark Chocolate (1 oz) ★	~12 mg	Lowest common caffeine source on this list — a reasonable pick if you want a small treat late in the day.	★ Best
Green Tea (8 fl oz) ★	~28 mg	About a third of brewed coffee's caffeine, plus L-theanine, which many people find produces a calmer alertness.	★ Best
Cola (12 fl oz)	34–40 mg	Added caffeine in most colas is a fraction of coffee's — diet and regular versions are usually similar.	Good
Black Tea (8 fl oz)	~47 mg	Roughly half of brewed coffee's caffeine per equivalent serving size.	Good
Espresso Shot (1 fl oz)	~63 mg	Concentrated by volume, but a single shot still delivers less total caffeine than an 8 oz brewed coffee.	Okay
Energy Drink (8 fl oz)	~80 mg (varies widely by brand)	Brand variance is large — some standard 12 oz cans exceed 160 mg. Always check the label of the specific product.	Okay
Brewed Coffee (8 fl oz)	70–140 mg (~95 mg typical)	Widest normal range of any common source — bean type, roast, and brew method all shift the actual amount.	Poor

Source: Caffeine content ranges aggregated from the Mayo Clinic Caffeine Content chart, the FDA's "Spilling the Beans: How Much Caffeine Is Too Much?" consumer guidance, and the Center for Science in the Public Interest (CSPI) Caffeine Chart. Brand, brewing method, and serving size cause real variance — always check a specific product's label for its exact caffeine content.

Worked Examples

Moderate Day: Coffee + Tea

Drinks Logged: 1 Brewed Coffee (8 oz, 95 mg) + 1 Black Tea (8 oz, 47 mg)

142 mg total (36% of FDA benchmark)

95 + 47 = 142 mg — well under the FDA's commonly cited 400 mg/day general benchmark for healthy adults.

Heavy Day: Exceeds the FDA Benchmark

Drinks Logged: 3 Espresso Shots (63 mg each) + 1 large Energy Drink (12 oz, 160 mg) + 1 Brewed Coffee (95 mg)

444 mg total (111% of FDA benchmark)

(63×3) + 160 + 95 = 189 + 160 + 95 = 444 mg — above the FDA's 400 mg/day general benchmark for healthy adults, raising the risk of jitteriness, elevated heart rate, and sleep disruption.

Half-Life Check: One Half-Life Elapsed

Dose: 200 mg
Hours Elapsed: 5
Half-Life Used: 5 hours (typical)

100 mg remaining (50%)

Remaining = 200 × 0.5^(5/5) = 200 × 0.5 = 100 mg — exactly one half-life has passed, so half the dose is still active.

Before-Bed Check: Afternoon Coffee

Dose: 95 mg (2:00 PM coffee)
Hours Elapsed: 8 (by 10:00 PM)
Half-Life Used: 5 hours (typical)

≈31 mg remaining (33%)

Remaining = 95 × 0.5^(8/5) = 95 × 0.5^1.6 ≈ 95 × 0.330 ≈ 31 mg — a small but non-zero amount is still active in your system 8 hours after a 2 PM coffee.

Pregnancy-Extended Half-Life

Dose: 100 mg
Hours Elapsed: 10
Half-Life Used: 15 hours (late-pregnancy estimate)

≈63 mg remaining (63%)

Remaining = 100 × 0.5^(10/15) ≈ 100 × 0.630 ≈ 63 mg — caffeine clears far more slowly than the typical 5-hour rate, which is why pregnancy guidance often recommends limiting total intake rather than relying on elapsed time.

How to Use This Calculator

1

Pick a mode

"Caffeine Content Tracker" totals up drinks you've had today; "Caffeine Remaining (Half-Life)" estimates how much caffeine is still active in your system.
2

Log your drinks

Choose a preset (coffee, espresso, tea, cola, energy drink, chocolate) or enter a custom amount, then click Add Drink for each one you've had.
3

Compare against the FDA benchmark

The running total is shown against the commonly cited 400 mg/day general benchmark for healthy adults, color-coded as you approach or pass it.
4

Switch to the half-life tab

Enter a dose in mg, hours elapsed since you drank it, and adjust the half-life if pregnancy, smoking, or another factor applies to you.
5

Read your remaining caffeine

See the estimated mg still active in your system, and optionally check it against a "safe before bed" threshold you set.

What Each Value Means

Caffeine Content (mg): The total milligrams of caffeine logged across every drink or food you've added, summed as a running daily total.
FDA Daily Benchmark (mg/day): A general guidance figure — commonly cited as 400 mg/day — that the FDA associates with a low likelihood of negative effects for most healthy, non-pregnant adults. Not a hard medical limit; individual tolerance varies.
Caffeine Half-Life (hours): The time it takes for the body to metabolize and clear half of an ingested dose of caffeine. Commonly cited as 5-6 hours, but the real range runs roughly 1.5-9.5 hours depending on individual factors like pregnancy or smoking.

Frequently Asked Questions

How much caffeine is safe per day?

The FDA commonly cites 400 milligrams a day as a general benchmark that's not typically associated with dangerous, negative effects for most healthy adults — roughly four to five 8 oz cups of brewed coffee. This isn't a strict medical limit, though: individual sensitivity varies a lot based on body weight, genetics (how fast your liver metabolizes caffeine), tolerance, and medications. Pregnant individuals are generally advised to stay well under this figure — ACOG guidance points to 200 mg/day or less.

How long does caffeine stay in your system?

Caffeine's half-life — the time for half of it to clear your bloodstream — is commonly cited around 5 to 6 hours in healthy adults, though the real range spans roughly 1.5 to 9.5 hours depending on the person. Using a 5-hour half-life, a 95 mg coffee leaves about 6 mg still active after 24 hours (five half-lives), which is why caffeine from an afternoon coffee can still affect sleep that night even though most of it is gone.

Does pregnancy or smoking change how fast caffeine clears?

Yes, significantly. Pregnancy slows caffeine metabolism — the half-life roughly doubles by the second trimester and can stretch to around 15 hours by the third trimester, which is part of why pregnancy guidance focuses on total daily intake rather than timing. Smoking has the opposite effect, speeding up the liver enzyme that breaks down caffeine and shortening the half-life by roughly 30-50%. Because of this, always use the half-life calculator's estimates as general information, not a substitute for guidance from your own doctor.

Why does energy drink caffeine content vary so much between brands?

Energy drinks aren't standardized the way brewed coffee roughly is — formulations differ widely by brand and can range from around 50 mg to well over 300 mg per can, especially in larger or "extra strength" sizes. An 8 oz serving averaging ~80 mg is a reasonable starting estimate, but a full 12 oz or 16 oz can from a high-caffeine brand can exceed 160-300 mg. Always check the Supplement Facts panel on the specific can you're drinking rather than relying on a category average.

Is this calculator a substitute for medical advice?

No. This tool provides general educational estimates based on published caffeine content ranges and a standard pharmacokinetic half-life formula — it does not account for your personal metabolism, medications, liver function, or health conditions. Pregnant or breastfeeding individuals, people with heart conditions or anxiety disorders, and anyone with a known caffeine sensitivity should follow their doctor's specific guidance rather than this calculator's general figures.