Evidence and editorial policy
Sources and editorial policy
We prefer systematic reviews, primary research, government guidance and first-party product data. Sources are linked so readers can inspect the evidence themselves.
FDA: Spilling the Beans — How Much Caffeine Is Too Much?
Consumer guidance and the often-cited 400 mg daily level for most healthy adults.
Drake et al. (2013): Caffeine Effects on Sleep
A controlled study of 400 mg caffeine taken 0, 3 or 6 hours before bedtime.
Gardiner et al. (2023): The Effect of Caffeine on Subsequent Sleep
A systematic review and meta-analysis examining how caffeine dose and timing affect subsequent sleep.
Clark and Landolt (2017): Coffee, Caffeine, and Sleep
A systematic review of epidemiological studies and randomised controlled trials.
Late-Afternoon and Evening Pre-Exercise Caffeine and Sleep (2025)
A systematic review and meta-analysis focused on caffeine before later training or competition.
Wikoff et al. (2017): The Safety of Ingested Caffeine
A comprehensive peer-reviewed review of caffeine safety and metabolism.
How drink data is recorded
Every drink record names a market and serving, links to its source, states its value basis and records when the source was reviewed. Current first-party exact values are preferred. Secondary-reported figures, indicative supplier guidance and older manufacturer approximations are used only when useful and defensible, and carry a prominent evidence warning wherever the number appears.
We do not convert a published range into a midpoint, infer caffeine from calories or transfer a formulation from another market. Browse the UK caffeine database, download its CSV data or inspect the machine-readable JSON.
How guides are produced
Each guide begins with a practical question that the calculator can answer transparently. Worked examples use the published exponential half-life formula, are checked against the calculator, and are labelled as estimates rather than measurements. Scientific claims are checked against sources relevant to that guide; article pages list those sources and their role.
Updates and corrections
Published and updated dates change only when the main content, calculations, sources or links change materially. Product caffeine values are taken from current manufacturer or public data where possible, but formulations vary by serving and market. Readers can report corrections through the contact link on the About page.
Independence and limitations
CaffCalc is maintained by an independent developer, not a medical practice. It does not sell supplements or accept payment for caffeine values. Some pages contain clearly labelled affiliate links, which do not influence the calculator’s formula, drink data or editorial conclusions.