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Free intermittent fasting timer

Start a 16:8 fast in one tap and watch your eating window and fat-burning phases in real time. No download, no sign-up, works offline.

Start fast00:00:00
  1. Fed
  2. Early fasting
  3. Fat burning
  4. Ketosis
  5. Deep ketosis

Free, no account, no app. Your timer and history stay in this browser.

Open the calculator

How the fasting timer works

Pick a protocol (16:8 is the most popular), tap start, and the timer tracks your fast in real time. As the hours pass, your body typically moves through several metabolic phases. These are general estimates and vary from person to person.

Metabolic phases during a fast

  • Fed — from about 0h
  • Early fasting — from about 4h
  • Fat burning — from about 12h
  • Ketosis — from about 16h
  • Deep ketosis — from about 24h