Last updated: September 24, 2026
What a cutoff time actually answers
A caffeine cutoff is the latest point in the day when one more planned drink still fits inside a target you have set for bedtime. It is a planning answer to a planning question, and it is specific to your own day. The amount you already have on board and the hour you intend to sleep both move the result.
Because of that, a cutoff is not a property of coffee in general. The same drink has an early cutoff on a day that already includes two coffees, and a much later one after a caffeine-free morning.
How the estimate is built
CaffCutoff derives the cutoff in four steps, using the same five-hour half-life that drives every other estimate on the site:
- 1. Project what is already there. Every drink you have logged is decayed forward to your bedtime, and the remainders are added together.
- 2. Work out the remaining room. That total is subtracted from the 25 mg bedtime planning target, which leaves the amount a new drink could still contribute.
- 3. Convert room into time. The calculator finds how long the planned dose needs in order to decay down to that remaining room.
- 4. Count back from bedtime. Subtracting that duration from your target bedtime produces the cutoff time.
If earlier intake has already used up the whole target, step two leaves nothing behind and the estimated cutoff falls before the current time. That is a real result rather than an error.
The 25 mg target is a planning value
CaffCutoff compares every bedtime estimate against 25 mg because it is a readable round number that marks a point where the remaining amount has become small. It is a product planning value chosen for this tool. It is not a clinical threshold, an exposure limit, or a guarantee about sleep.
The report page separately shows a 5 mg clearance estimate for the point where the model has fallen much further. Both numbers exist to make the output comparable from one day to the next.
Worked examples
Every row below assumes a five-hour half-life, the 25 mg bedtime planning target, and one planned drink of the size shown. Times are rounded to the minute.
| Already logged | Planned drink | Bedtime | Estimated cutoff |
|---|---|---|---|
| Nothing | 95 mg coffee | 23:00 | 13:22 |
| Nothing | 63 mg espresso | 23:00 | 16:20 |
| Nothing | 150 mg pre-workout | 23:00 | 10:05 |
| Nothing | 95 mg coffee | 22:00 | 12:22 |
| 95 mg at 09:00 | 95 mg coffee | 23:00 | 07:41 |
| 28 mg at 14:00 | 95 mg coffee | 23:00 | 10:34 |
The last two rows show how strongly earlier intake pulls the cutoff forward. A single morning coffee leaves roughly 11 mg of room, which a 95 mg drink needs more than fifteen hours to reach.
Why the cutoff moves from day to day
- Your bedtime. Going to bed an hour later gives every drink in the day one extra hour of decay, which pushes the cutoff later.
- What is already logged. Earlier drinks compete for the same target, and the most recent one competes hardest.
- Size of the planned drink. A larger dose takes longer to fall to the same small amount, so it needs an earlier start.
- The half-life assumption. A longer half-life stretches every one of those durations, moving the cutoff earlier still.
If the cutoff has already passed
The estimate is still useful information. It means that adding the planned drink would push the bedtime total above the planning target. Common responses are to pick a smaller serving, to accept a higher bedtime number for that day, or to log the drink anyway so the estimate stays honest.
None of those is a rule, and the calculator has no opinion about whether a later coffee is a good idea. It only keeps the arithmetic consistent.
Why a variable cutoff beats a fixed hour
A fixed cutoff hour has the appeal of being easy to remember, but it ignores everything that makes the answer different from one person to the next and from one day to the next. Someone who finishes a last coffee at noon and sleeps at 23:00 lands in a very different place from someone who takes a pre-workout at 18:00 and sleeps at the same hour. Deriving the cutoff from the day itself keeps the output tied to what you actually drank.
Common questions
Is there an official caffeine cutoff time?
No. Published advice often suggests a fixed hour, but a cutoff depends on how much caffeine is already in your system, how much you plan to drink, and when you intend to sleep. CaffCutoff estimates a cutoff from those inputs instead of applying one rule to everyone.
Why does the calculator say my cutoff has already passed?
Because earlier drinks already fill most of the planning target. When the caffeine still on board at bedtime is close to or above 25 mg, there is very little room left for another drink, so the estimated cutoff falls in the past.
Should I watch the cutoff time or the remaining amount?
They describe the same math from two directions. The remaining amount shows where your day currently lands at bedtime, while the cutoff shows the latest start time for one more planned drink. Use whichever answers the question you are actually asking.
Does a decaf drink really move the cutoff?
Barely. A decaf serving retains only a small amount of caffeine, so it usually changes the bedtime estimate by well under a milligram. It is still logged the same way if you want the total to be complete.
Related reading
- Caffeine Half-Life: How Long Caffeine Stays in Your System
- Caffeine Metabolism: How Your Body Clears Caffeine
- Caffeine Content Chart for Common Drinks
- Coffee Before Bed: How Late Is Too Late to Drink Coffee?
- What Changes Caffeine Half-Life?
- Am I a Slow Caffeine Metabolizer? A Self-Check
- How Much Caffeine Is Left? Dose by Hour Chart
- How Much Caffeine Is Left at Bedtime?
Run your own numbers
The CaffCutoff calculator turns these ideas into an estimate for your own day: add each drink, set a target bedtime, and read the remaining caffeine, the cutoff estimate, and the decay timeline.