Know the starting dose
How much caffeine is in coffee, tea, and energy drinks?
A useful decay estimate begins with milligrams. Drink type, product, preparation, and serving size all affect that starting number.
Checked against authoritative sources
Evidence reviewed 6 August 2026 · 8 minute read
General education, not individual medical advice.
The short answer
Caffeine content varies widely by product and serving size. Use a manufacturer value when available, include the whole container, and use a range for unmeasured coffee or tea.
Coffee values span a wide range
The FDA lists a broad caffeine range for regular brewed coffee. Product, preparation, and serving size all affect the amount, and café sizes can contain different numbers of espresso shots.
When a chain publishes nutrition data, use the exact drink and size. At home, use a cautious range unless you have a tested product value.
Sources for this section: U.S. Food and Drug Administration.
Tea still belongs in the daily total
FDA examples show that green and black tea can contain caffeine, while individual products and serving sizes vary. Bottled tea may state an amount on the label or manufacturer's site.
Several smaller servings add together across the day. Record the available milligrams instead of treating tea as negligible because it feels gentler.
Sources for this section: U.S. Food and Drug Administration.
Read the entire energy-drink container
Energy drinks span a wide caffeine range. Some labels state a value per serving while the can contains multiple servings. Guarana and other caffeine-containing ingredients still contribute to the total.
The FDA reports that medical experts advise against energy drinks for children and teenagers. Concentrated caffeine products deserve particular caution because small volume does not mean small dose.
Sources for this section: U.S. Food and Drug Administration.
Caffeine turns up outside the drinks aisle
Chocolate, bars, gum, supplements, pre-workout powders, and some over-the-counter medicines can contain caffeine. The source does not change the basic need to count the milligrams.
If a supplement uses a proprietary blend and does not disclose the caffeine amount, a precise bedtime estimate is impossible. That uncertainty is information, not an invitation to type a confident guess.
Sources for this section: U.S. Food and Drug Administration.
How to log an uncertain drink
Enter the most credible central estimate, then run the calculation again at a plausible high value. If both lead to the same timing decision, the uncertainty does not matter much. If the decision changes, choose the more cautious timing or get better product information.
Save the exact product and size when you repeat a drink. A useful personal log becomes faster over time because you stop rebuilding the same estimate.
- Prefer label or manufacturer values.
- Match the precise serving size.
- Compare a low and high estimate when the amount is unknown.
Keep the bedtime estimate beside the daily total
The half-life tool answers what may remain later. It does not track whether the day's total fits public-health guidance. Keep both numbers visible.
For most healthy adults, the FDA cites 400 mg per day as an amount not generally associated with negative effects. EFSA notes single doses of 100 mg can still affect sleep in some adults near bedtime. One number does not replace the other.
Sources for this section: U.S. Food and Drug Administration, European Food Safety Authority.
How to record a drink with an uncertain amount
Start with the product's own information. If a 500 ml bottle states 32 mg per 100 ml, the full bottle contains 160 mg. If a café publishes caffeine by drink and size, match both. These are stronger inputs than a generic database average.
For an unmeasured home coffee, record the preparation and serving consistently and use a range. Run the bedtime estimate at both ends. A conclusion that changes across the range means the available dose information cannot support a precise cutoff.
- Save recurring drinks by exact product and size.
- Update the entry when a recipe, number of shots, or container changes.
- Keep caffeine amount separate from calories, sugar, or serving volume; they answer different questions.
Sources for this section: U.S. Food and Drug Administration.
Common questions
How much caffeine is in one coffee?
There is no single amount. The FDA lists a wide range for brewed coffee, and size and preparation matter. Use the café or product value when available.
Does decaf contain caffeine?
Usually a small amount. Treat decaf as much lower caffeine, not automatically zero.
Is natural caffeine different from added caffeine?
For safety and intake counting, the FDA says the body handles naturally occurring and added caffeine the same way.
Sources and review notes
We favour public-health guidance, clinical bodies, official statistics, and original research. Source links are provided so you can inspect the wording and boundaries yourself.
- 01Spilling the Beans: How Much Caffeine is Too Much?U.S. Food and Drug Administration
- 02Caffeine: safety guidance for adults and pregnancyEuropean Food Safety Authority