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Free caffeine timing tool

Caffeine half-life calculator

Enter a dose and two times to compare faster, average, and slower elimination scenarios.

Free to use·No account required·Evidence checked 6 August 2026
mg

If the target time is earlier on the clock, the calculator treats it as the following day. Equal times mean zero elapsed hours. Generic drink amounts vary; use the product label when possible.

This tool is limited to ordinary planning inputs of 0–500 mg. That range is a calculator boundary, not a statement that any dose is safe.

Estimated after 8.5 hours

6mg2-hour half-life · 5% remains
28mg4-hour half-life · 23% remains
57mg8-hour half-life · 48% remains

These are mathematical scenarios, not measured blood levels or sleep predictions. EFSA describes an adult average around four hours and a typical range of roughly two to eight hours; individual clearance can fall outside a simple model.

Formula: remaining dose = starting dose × 2−(hours ÷ half-life). The model assumes the full dose is immediately available and ignores the absorption phase, so it is weakest soon after consumption. No result is labelled safe or unsafe.

How the calculation works

For each scenario, the starting dose is multiplied by two raised to the negative number of elapsed half-lives. After one half-life, 50% remains; after two, 25%; after three, 12.5%.

The tool compares two, four, and eight hours. EFSA describes about four hours as an adult average and roughly two to eight hours as a typical range. An older National Academies review reports wider individual values.

Sources: European Food Safety Authority, National Academies Press via NCBI Bookshelf.

Getting a useful starting dose

Use the caffeine amount printed on the product or published by the manufacturer. Coffee and tea vary by preparation and serving size, so a generic preset is only an example.

The tool accepts one dose at a time. Run each drink separately when you have several, then add the estimates for the same target time because their remaining amounts overlap.

Sources: U.S. Food and Drug Administration.

How to interpret the result

The number is estimated caffeine remaining, not a blood concentration and not a prediction of whether you will sleep. Compare scenarios and look for decisions that stay sensible across the range.

Public-health daily-intake guidance answers a different question. EFSA notes that even 100 mg close to bedtime may affect sleep in some adults.

Sources: European Food Safety Authority.

Important limits

The model assumes the full dose is immediately available and omits the absorption phase. It also has no information about your metabolism, medicines, health conditions, pregnancy-related clearance, tolerance, sensitivity, or the true dose of an unmeasured drink.

The result is unsuitable for overdose, medication, pregnancy, driving, or other safety decisions. Speak with a qualified professional for personal medical guidance.

If the amount was large or unknown, or symptoms are severe, seek urgent help from local medical or poison-control services.

Sources: U.S. Food and Drug Administration, European Food Safety Authority.

Sources

  1. 01Spilling the Beans: How Much Caffeine is Too Much?U.S. Food and Drug Administration
  2. 02Caffeine: safety guidance for adults and pregnancyEuropean Food Safety Authority
  3. 03Pharmacology of CaffeineNational Academies Press via NCBI Bookshelf · 2001

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Caffeine and sleep

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