DozeClock › Caffeine › Green tea

Green tea before bed: 28 mg of caffeine and how long it lasts

Updated October 5, 2026 · Sources: Mayo Clinic · U.S. Department of Agriculture · U.S. Food and Drug Administration · Foods · National Academies Press

Short answer

28 mg

per 8 fl oz (237 ml)

0 h 49 min

until under 25 mg is left

A brewed cup of green tea carries 28 mg, which the model clears below 25 mg in about 49 minutes. One cup is a short clock. Refills and bottles are where the evening total gets away from you.

Range in site data25–29 mgby brand, brew and size

Share of the FDA's 400 mg a day7%one serving, healthy adults

General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.

Small dose

At 28 mg this is the lowest-clock drink here, and it can feel harmless. The sum is what counts: three cups is 84 mg, which the model clears under 25 mg in about 8 h 45 min, longer than a single espresso shot would need. Decide how many cups before the first one.

Caffeine left after one green tea (28 mg)

Model: remaining = dose × 0.5^(hours ÷ 5). Half-life 5 h (Institute of Medicine 2001); real half-lives run 1.5–9.5 h between people.

After 5 hours about 14 mg of the 28 remain, after 10 hours about 7. The 25 mg line is crossed at 49 minutes. This is a single cup; doses add, so a second cup poured an hour later restarts the count from a higher floor. On the slowest half-life people have shown (9.5 hours, Institute of Medicine 2001), about 19 mg would still be left 5 hours after the cup.

01Last green tea by bedtime

Bedtime	Finish by (25 mg left)	Left at lights out if finished 6 h before	Left if finished 3 h before
9:00 pm	8:10 pm	12 mg	18 mg
9:30 pm	8:40 pm	12 mg	18 mg
10:00 pm	9:10 pm	12 mg	18 mg
10:30 pm	9:40 pm	12 mg	18 mg
11:00 pm	10:10 pm	12 mg	18 mg
11:30 pm	10:40 pm	12 mg	18 mg
12:00 am	11:10 pm	12 mg	18 mg
12:30 am	11:40 pm	12 mg	18 mg
1:00 am	12:10 am	12 mg	18 mg

Finish-by times are rounded down to 5 minutes. 25 mg is this site's planning line, not a clinical threshold. Every drink at once: caffeine cutoff grid.

02Brewed, bottled and powdered: the same leaf, different doses

The USDA lists brewed regular green tea at 12 mg per 100 g, with a measured spread of 8 to 18 across 6 data points. USDA gives a cup as 245 g, so one cup is about 29 mg, and 237 g (8 fl oz) is 28. Across the measured spread that is 19 to 43 mg. The FDA puts green tea at 37 mg per 12 fl oz, inside the 28 to 64 mg the USDA spread implies for that size.

Unlike black tea, green tea did not change with the tea bag in a 2025 lab study of tea infusions: serving method had no effect on green tea, and its average came out at 11 mg per 200 mL. In other words, a cup of green tea is a reasonably steady number from the kettle, which suits a clock built on one figure.

Bottles break that steadiness. USDA lists unsweetened ready-to-drink green tea at 12 mg per 100 g, so a 16 fl oz bottle is about 57 mg, double a brewed cup and more than a cup of black tea. Sweetened bottled green tea is much lower, about 5 mg per 100 g, near 14 mg for a 270 g cup. Decaffeinated brewed green tea is listed at 0 mg.

Serving or brew	Caffeine	Basis	Source
8 fl oz green tea (headline figure)	28 (25–29)	Typical figure from the Mayo Clinic caffeine chart, as stored in the site data	Mayo Clinic
8 fl oz brewed, 237 g	28 (19–43)	12 mg per 100 g, measured range 8–18, 6 data points; multiplied by 237 g	USDA FDC 171917
1 cup brewed, 245 g	29 (20–44)	Same USDA figures multiplied by the 245 g cup USDA lists	USDA FDC 171917
12 fl oz brewed, 355 g	43 (28–64)	Same USDA figures multiplied by 355.2 g (12 × 29.6 g per fl oz)	USDA FDC 171917
12 fl oz green tea	37	FDA consumer update, per 12 fl oz serving	FDA
200 mL green tea infusion	11 ± 2.1	Lab measurement, mean ± SD across the study's brew times and temperatures	Foods 2025
16 fl oz bottled, unsweetened	57	12 mg per 100 g; multiplied by the 473 g USDA lists for 16 fl oz	USDA FDC 171911
1 cup bottled, sweetened, 270 g	14	5 mg per 100 g (2 data points); multiplied by the 270 g USDA lists for a cup	USDA FDC 174128
8 fl oz brewed decaffeinated	0	USDA lists 0 mg per 100 g	USDA FDC 171910

Per-serving values from USDA mg per 100 g are calculated by DozeClock using the USDA gram weight of a fluid ounce (29.6 g) or the portion USDA lists; they are not measured values for those sizes. The Foods 2025 figure is copied from the study abstract and describes lab brews.

03Green tea next to the three nearest drinks

Drink	Serving	mg	Hours to under 25 mg	Finish by for an 11 pm bed
Black tea	8 fl oz (237 ml)	47	4 h 33 min	6:25 pm
Cola	12 fl oz (355 ml) can	33	2 h	8:55 pm
Green tea	8 fl oz (237 ml)	28	0 h 49 min	10:10 pm
Dark chocolate	1 oz (28 g)	24	0 h	any time

mg per serving, not per ounce: servings differ in size · nearest = smallest difference in mg per serving (data/caffeine.json)

Dark chocolate at 24 mg and green tea at 28 mg are four apart, yet one is an ounce of solid and the other a mug of liquid. Per fluid ounce, green tea carries 3.5 mg against cola at 2.8. Black tea sits 19 mg above, which on this page's clock means nearly four extra hours of waiting. If green tea is the evening default, keep to cups, not bottles.

Sources

Caffeine content for coffee, tea, soda and more — Mayo Clinic (figure stored in DozeClock data; page not re-fetched on 2026-10-05)
FoodData Central: Beverages, tea, green, brewed, regular (SR Legacy, FDC ID 171917; also 171910, 171911 and 174128) — U.S. Department of Agriculture
Spilling the Beans: How Much Caffeine is Too Much? — U.S. Food and Drug Administration
Determination of L-Theanine and Caffeine Contents in Tea Infusions with Different Fermentation Degrees and Brewing Conditions Using the Chromatographic Method — Foods (Basel), 2025
Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations — National Academies Press, 2001