Caffeine Cut-off Calculator
Plan a caffeine cut-off from dose and bedtime using half-life and a residual target, then check a proposed drink time and daily total.{{ summaryTitle }}
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| Scenario | Clock time | Lead | Residual at bed | Safe max dose | Status | Copy |
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First-order planning model
- Required half-lives
- {{ formatNumber(computation.values.required_half_lives, 3) }}
- Decay time
- {{ formatDuration(computation.values.decay_min) }}
- Model boundary
- Dose at or below the target needs no decay time, but absorption and buffer still apply.
A late coffee can outlast its obvious lift. Caffeine is absorbed fairly quickly, but the body clears it gradually. Its half-life is the time needed for the active amount to fall by half, so a 100 mg serving does not become zero after one half-life. About 50 mg remains, then about 25 mg after another half-life under a simple first-order model.
Sleep timing depends on both dose and clearance. A larger serving needs more time to fall to the same bedtime amount, while a longer half-life stretches every step of the decline. Product labels and cafe recipes also vary, so the milligrams in the actual drink are more useful than a generic cup count.
- Residual caffeine
- The modeled amount from one serving that remains at bedtime.
- Cut-off
- The latest drink time that reaches a chosen residual target after allowing for absorption and any extra planning buffer.
- Daily intake
- The sum of the planned serving and caffeine already consumed that day. It answers a different question from bedtime residual.
Those distinctions matter because staying under a general daily guide does not guarantee good sleep, and meeting a bedtime target does not establish a safe personal dose. Sensitivity and clearance can change with pregnancy, medicines, smoking, liver function, age, and sleep disorders. A cut-off estimate is therefore a planning aid, not a promise that sleep will be unaffected.
The most useful starting point is conservative and repeatable. Use the labeled dose when available, keep bedtime and assumptions stable for several nights, and move the cut-off earlier if sleep onset, awakenings, or next-day alertness remain worse than expected.
How to Use This Tool:
Model one planned serving first. The optional candidate and daily-guide fields add comparisons without changing the main cut-off calculation.
- Choose a Drink preset or enter the serving's labeled Caffeine dose, then set the local Target bedtime.
- Select a Half-life profile and Bedtime target. Use custom values only when a clinician or a deliberate personal planning rule gives you a better assumption.
- Adjust Absorption time and Extra buffer when needed. Both move the latest planned sip earlier.
- Enter a Candidate drink time to test it. Add Consumed earlier today and a Daily guide comparison only when you also want a daily-total check.
- Read Latest planned sip and Lead first. In Candidate check, compare the proposed time's residual and safe-dose estimate with the selected bedtime target.
Interpreting Results:
Latest planned sip is the boundary produced by the selected dose, bedtime, half-life, absorption time, residual target, and buffer. A candidate with a nonnegative time margin fits those assumptions; a negative margin reports how late it is.
- Candidate residual estimates how much of that one serving remains at bedtime.
- Safe max dose reverses the same model to estimate the largest serving that fits the candidate time.
- Daily total adds earlier intake to the planned dose, but earlier servings are not added to the residual timeline.
- The six-hour row is a comparison point, not a universal rule. Dose, half-life, absorption, and target can make the calculated cut-off earlier or later.
Meeting the target means only that the modeled residual is at or below a user-selected amount. If that creates false confidence, compare the result with your own sleep response and use a longer half-life, lower target, or larger buffer.
Technical Details:
The calculation treats absorption as a linear rise to the full dose, followed by first-order exponential elimination. It is a transparent one-compartment planning model, not a measurement of blood concentration. The practical cut-off works backward from bedtime and reserves absorption time before the modeled decay interval.
Formula Core:
The required lead time is the absorption reserve plus enough half-lives to reach the residual target, followed by any extra buffer.
D is dose in milligrams, T is the bedtime residual target in milligrams, h is half-life in hours, a is absorption time in minutes, b is the added buffer in minutes, L is total lead time, and l is the candidate's lead time. When dose is at or below the target, n is zero and the cut-off still reserves absorption and buffer time. When candidate lead is no longer than absorption plus buffer, safe dose equals the target.
Before absorption completes, the residual curve uses a linear ramp from zero to the full dose. Afterward it uses the exponential equation above. The buffer changes the cut-off and safe-dose comparison, but it does not claim to change caffeine metabolism.
A 95 mg serving, 30 mg target, 5-hour half-life, and 45-minute absorption reserve require about 1.663 half-lives. Decay takes about 499 minutes, total lead time is about 544 minutes, and a 10:00 PM bedtime produces a cut-off near 12:56 PM. At the six-hour comparison point, the same serving leaves about 45.9 mg under the model.
Rules and Boundaries:
| Quantity | Supported rule | Effect |
|---|---|---|
| Dose | 0.1 to 1,000 mg | Larger doses require more decay time when they exceed the target. |
| Half-life | 1 to 15 hours | Longer values move the cut-off earlier in direct proportion to required half-lives. |
| Residual target | 1 to 200 mg | Lower targets make the plan more conservative. |
| Candidate clock | The next occurrence before bedtime within a 24-hour cycle | A candidate later than the bedtime clock is treated as occurring on the preceding side of the overnight interval. |
| Daily guides | No comparison, 200 mg, 300 mg, or 400 mg | Earlier intake plus the planned dose is compared with the selected guide; this does not rebuild the residual curve. |
Calculations retain full precision. Clock times and durations are rounded to the nearest minute for display, while caffeine amounts show one decimal below 100 mg and whole milligrams at 100 mg or more.
Health and Model Limits:
This estimate is informational and cannot set a personal medical limit or predict sleep quality. It models one planned serving and does not combine the timing of earlier servings, measure blood caffeine, or account for tolerance and individual pharmacokinetics.
- Drink presets are approximate. Prefer the product label or a reliable menu value.
- Pregnancy, liver disease, medicines, smoking, age, and other factors can materially change caffeine clearance.
- The 10 to 40 mg bedtime targets are planning assumptions, not clinical thresholds.
- General daily guides do not replace advice from a clinician who knows your pregnancy, medicines, cardiovascular history, anxiety, or sleep condition.
References:
- Caffeine, StatPearls, NCBI Bookshelf, 2024.
- Spilling the Beans: How Much Caffeine is Too Much?, U.S. Food and Drug Administration, 2024.
- How much coffee can I drink while pregnant?, American College of Obstetricians and Gynecologists, 2020.
- Caffeine Effects on Sleep Taken 0, 3, or 6 Hours before Going to Bed, Journal of Clinical Sleep Medicine, 2013.