Add every caffeine source you had today, from gum and coffee to energy drinks and tablets, and this calculator totals the milligrams, checks them against the adult and pregnancy limits, estimates how much is still in your blood at bedtime, and tells you the latest clock time for one more dose. Every preset value and limit below is tied to a source you can open.
Not medical advice. The half-life model is a population average; measured caffeine half-lives in healthy adults run from about 2.7 to 9.9 hours, so treat the bedtime numbers as an estimate, not a lab result.
1. What you had today
| Source | Custom mg | How many | Time (24 h) | mg |
|---|
Preset values: gum from the brand product pages (Neuro Gum 40 mg and Extra Strength 100 mg, Military Energy Gum 100 mg, Run Gum 50 mg, Rev Gum 60 mg and Extra Strength 100 mg); brewed coffee, espresso, black tea, green tea and cola from USDA FoodData Central SR Legacy entries scaled to the serving size (cola uses the FDC mean of 9 mg per 100 g, so 33 mg per 12 oz can rather than the 34 mg often quoted); Red Bull 80 mg per 8.4 oz and Monster 160 mg per 16 oz from the brand pages; 5-hour Energy Extra Strength 230 mg from the brand product page and its DSLD label (the brand does not print a milligram figure for Regular Strength); caffeine tablet 200 mg from the NoDoz DailyMed label. Links are in the Sources section.
2. About you
Half-lives measured in healthy adults span roughly 2.7 to 9.9 hours (Blanchard and Sawers 1983). Pregnancy stretches the half-life to about 10.5 hours by the last month, chronic low-dose oral contraceptives lengthen it from about 5.4 to 7.9 hours, the antibiotic ciprofloxacin from about 5.2 to 8.2 hours, and liver disease also slows clearance (PubMed sources below). If any of those apply, pick Slow.
3. Your numbers
How the math works
Caffeine leaves the blood by first-order decay: every half-life, whatever is left drops by half. The calculator sums each dose times 0.5 raised to the power of hours until bedtime divided by your half-life. Two Neuro pieces at 08:00 and a coffee at 13:00, bedtime 23:00, half-life 5 hours: 80 x 0.5^3 + 95 x 0.5^2 = 10 + 23.75, about 34 mg.
The half-life is the weak point. In a crossover study of ten healthy men it ran from 2.7 to 9.9 hours (Blanchard and Sawers 1983), which is why the tool offers 3, 5 and 8 hour settings. The cutoff card runs the decay backwards: it finds the latest time one more dose could go in while the bedtime total stays under 100 mg, the single dose EFSA says may affect sleep duration and patterns in some adults when taken close to bedtime (EFSA 2015). In a home study, 400 mg taken even 6 hours before bed measurably shortened total sleep time (Drake 2013).
Why gum is different
Swallowed caffeine has to reach the small intestine before it is absorbed. Gum releases caffeine in the mouth, where part of it crosses the buccal mucosa straight into the bloodstream. In the pharmacokinetic study behind most gum claims, time to peak plasma level was 44 to 80 minutes for gum versus 84 to 120 minutes for capsules at the same doses (Kamimori 2002). The onset card uses those windows for whichever source you logged last.
A later study found two plasma peaks after caffeinated gum, one from the mouth and one from the gut, with release rising as chewing went from 2 to 5 to 10 minutes (Morris 2019). The gum used in the military trials delivered 85 percent of its 100 mg in 5 minutes of chewing (Bellar 2011). So chew for at least 5 minutes, and count a piece as its full label dose.
Limits people actually use
- 400 mg per day, healthy adults. The FDA cites 400 mg a day as an amount not generally associated with negative effects; EFSA reaches the same 400 mg (about 5.7 mg per kg) for daily intake spread through the day.
- 200 mg in one sitting, or 3 mg per kg. EFSA’s single-dose reference for healthy adults, including doses taken less than two hours before intense exercise. The tool shows your largest logged dose against both.
- 200 mg per day in pregnancy and while breastfeeding. EFSA’s figure for intakes that do not raise safety concerns for the foetus. Toggle it on and the daily bar drops to 200 mg.
- Adolescents. EFSA proposes 3 mg per kg per day for habitual intake by children and adolescents. The American Academy of Pediatrics goes further and states that caffeine and other stimulants in energy drinks have no place in the diet of children and adolescents.
- Toxic range. The FDA estimates toxic effects such as seizures can be observed with rapid consumption of around 1,200 mg. The tool warns above 400 mg inside any 3 hour window and again above 1,000 mg in a day.
Sources
- Blanchard and Sawers 1983, absolute bioavailability of caffeine (half-lives 2.7 to 9.9 h)
- Kamimori 2002, caffeine gum versus capsules (Tmax 44 to 80 vs 84 to 120 min)
- Morris 2019, caffeine release and absorption from caffeinated gums
- Bellar 2011, low-dose caffeine gum and perceived pain (85 percent of 100 mg in 5 minutes)
- Drake 2013, caffeine taken 0, 3 or 6 hours before bed
- American Academy of Pediatrics 2011, sports drinks and energy drinks for children and adolescents
- Knutti 1982, pregnancy and caffeine half-life; Abernethy 1985, oral contraceptives; Healy 1989, ciprofloxacin; Nehlig 2018, factors affecting caffeine metabolism including liver disease
- FDA, Spilling the Beans: How Much Caffeine Is Too Much? (400 mg; toxic effects around 1,200 mg)
- EFSA, Caffeine topic page summarising the 2015 Scientific Opinion (400 mg per day, 200 mg single, 3 mg per kg, 100 mg and sleep, 200 mg in pregnancy)
- USDA FoodData Central: brewed coffee, espresso, black tea, green tea, cola
- DailyMed, NoDoz Alertness Aid label (caffeine 200 mg per caplet); NIH DSLD, 5-hour Energy Extra Strength label (230 mg caffeine)
- Brand pages: Neuro Gum, Neuro Extra Strength, Military Energy Gum, Run Gum, Rev Gum, Rev Gum Extra Strength, Red Bull, Monster Energy, 5-hour Energy Extra Strength
What most people ask next
- Caffeine cutoff calculator: the bedtime question on its own, with more half-life options
- Pre-workout stack calculator: caffeine plus the other doses that go into a training stack
- L-theanine dose calculator: the pairing most caffeine gums already include
- Best supplements for energy and fatigue: what to reach for when caffeine is not the answer
- Sleep supplement protocol: the other half of the caffeine equation
- Do sleep gummies actually work?
- Can I take creatine with caffeine?
- All UsefulVitamins calculators and tools
FAQ
How much caffeine is in Neuro Gum?
The brand pages list 40 mg of natural caffeine per piece for Neuro Energy and Focus gum and mints, and 100 mg per piece for the Extra Strength version. Two regular pieces roughly match one 8 oz brewed coffee (95 mg per USDA FoodData Central).
How fast does caffeine gum work compared with coffee?
In the Kamimori 2002 pharmacokinetic study, gum reached peak plasma caffeine in 44 to 80 minutes versus 84 to 120 minutes for capsules, a difference the authors said may indicate absorption through the lining of the mouth (the buccal mucosa).
How much caffeine is too much in a day?
The FDA cites 400 mg a day as an amount not generally associated with negative effects for most adults, and EFSA reaches the same figure. EFSA sets 200 mg per day for pregnancy and breastfeeding, and 3 mg per kg for children and adolescents. The FDA estimates toxic effects such as seizures around 1,200 mg consumed rapidly.
When should I stop drinking caffeine before bed?
It depends on the dose and your half-life, which is what the cutoff card computes. As a rule of thumb, a single 200 mg tablet at 18:00 with a 5 hour half-life still leaves 100 mg at 23:00, the level EFSA associates with sleep effects, and Drake 2013 found 400 mg disrupted sleep even when taken 6 hours before bed.
How long does caffeine last in your system?
Blanchard and Sawers 1983 measured plasma half-lives from 2.7 to 9.9 hours in healthy adults, so a 100 mg dose can take anywhere from about 8 hours to close to 30 hours to fall below 13 mg. Pregnancy, oral contraceptives, ciprofloxacin and liver disease all lengthen the half-life.
