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Decaf coffee before bed: 2 mg of caffeine and how long it lasts
Updated October 5, 2026 · Sources: U.S. Food and Drug Administration · U.S. Department of Agriculture · U.S. Department of Agriculture · U.S. Department of Agriculture
Short answer
2 mg
per 8 fl oz (237 ml)
0 h
already under 25 mg
At 2 mg a cup, decaf is already under the 25 mg line when you finish it. The 15 mg end of the FDA range is where the arithmetic starts to matter.
General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.
At 2 mg there is nothing to wait out, so the finish-by column reads "any time". That holds for one cup. The FDA says decaf has "some caffeine" and that people who react strongly may want to avoid it altogether.
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.
Starting from 2 mg, the line is flat on this chart: it begins under 25 mg and only moves toward zero. Half of 2 mg is 1 mg after 5 hours. The curve is more useful as a reminder that decay works on the total, not on each cup. If you drink several cups close together the amounts add first and then decay as one pile, which is why the table further down counts cups rather than hours.
01Last decaf coffee 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 | any time | 1 mg | 1 mg |
| 9:30 pm | any time | 1 mg | 1 mg |
| 10:00 pm | any time | 1 mg | 1 mg |
| 10:30 pm | any time | 1 mg | 1 mg |
| 11:00 pm | any time | 1 mg | 1 mg |
| 11:30 pm | any time | 1 mg | 1 mg |
| 12:00 am | any time | 1 mg | 1 mg |
| 12:30 am | any time | 1 mg | 1 mg |
| 1:00 am | any time | 1 mg | 1 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.
02Where decaf stops being small
The FDA puts decaf coffee at 2 to 15 mg in an 8 fl oz cup and states plainly that decaffeinated does not mean caffeine-free. The headline 2 mg is the low end of that range. USDA agrees on the low side: it lists brewed decaf at 1 mg per 100 g, a whole-number value that works out to about 2 mg for a 237 g cup.
The spread comes from the beans and the process, and a menu will not tell you. A cafe cup could sit anywhere from 2 to 15 mg, so plan on the high end if you are sensitive. One cup at 15 mg is still under 20 percent of a regular brewed cup, and a single cup at that level is also under the 25 mg planning line.
Cups stack. Four cups at the 2 mg end is 8 mg; four at the 15 mg end is 60 mg, roughly a regular cup of coffee drunk in installments. Six cups at 15 mg is 90 mg, and that pile takes about 9 hours to fall under 25 mg. Nobody needs to count one cup of decaf, but an evening of them is worth a quick tally.
Instant decaf follows the same pattern. USDA lists decaf instant powder at 122 mg per 100 g, so a rounded teaspoon of about 1.8 g carries about 2 mg.
| Serving or brew | Caffeine | Basis | Source |
|---|---|---|---|
| 8 fl oz decaf (headline figure) | 2 (2–15) | FDA: "decaf coffee typically has 2 to 15 milligrams in an 8-fluid-ounce cup" | FDA |
| 8 fl oz brewed decaf, 237 g | 2 | 1 mg per 100 g (USDA, whole-number value) multiplied by 237 g, calculated by DozeClock | USDA FDC 171889 |
| Decaf instant, 1.8 g rounded teaspoon | 2 | 122 mg per 100 g multiplied by 1.8 g, calculated by DozeClock | USDA FDC 174133 |
| 4 cups at the low end | 8 | 4 × 2 mg, calculated by DozeClock | FDA |
| 4 cups at the high end | 60 | 4 × 15 mg, calculated by DozeClock | FDA |
| 6 cups at the high end | 90 | 6 × 15 mg; about 9 h 15 min to fall under 25 mg, calculated by DozeClock | FDA |
| Regular brewed coffee, 8 fl oz, for scale | 95 | 40.0 mg per 100 g (USDA FDC 171890) multiplied by 237 g | USDA FDC 171890 |
Cup-count rows multiply the FDA range and are calculated by DozeClock; real cups vary by beans and process. The FDA page does not say how the 2 to 15 mg range was measured.
03Decaf coffee next to the three nearest drinks
| Drink | Serving | mg | Hours to under 25 mg | Finish by for an 11 pm bed |
|---|---|---|---|---|
| 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 |
| Decaf coffee | 8 fl oz (237 ml) | 2 | 0 h | any time |
mg per serving, not per ounce: servings differ in size · nearest = smallest difference in mg per serving (data/caffeine.json)
Decaf sits at the bottom of the caffeine list in the site data. The nearest drinks in the table are all far larger, so the real comparison is decaf at 15 mg against regular coffee at 95 mg: about one sixth, not zero.
Sources
- Spilling the Beans: How Much Caffeine is Too Much? — U.S. Food and Drug Administration
- FoodData Central: Beverages, coffee, brewed, prepared with tap water, decaffeinated (SR Legacy, FDC ID 171889) — U.S. Department of Agriculture
- FoodData Central: Beverages, coffee, instant, decaffeinated, powder (FDC ID 174133) — U.S. Department of Agriculture
- FoodData Central: Beverages, coffee, brewed, prepared with tap water (FDC ID 171890) — U.S. Department of Agriculture
General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.