Fasted FASTED

Autophagy Calculator

The estimate starts at hour 18 of the fast and moves from there: a low-carbohydrate last meal takes 2 hours off, a high-carbohydrate one adds 2, training takes off 1.5, being over 50 adds 1. The result is clamped between 16 and 24 hours. It cannot be measured outside a laboratory, and the method below says exactly that.

Autophagy begins in

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Start your fast to begin tracking

0% to autophagy

Fasting Phases

🍽

Fed

0-4h

▼

Catabolic

4-8h

🔥

Fat Burning

8-12h

⚡

Ketosis

12-18h

♻

Autophagy

18-24h

✨

Deep

24h+

Autophagy Onset

18h

--

Deep Autophagy

24h

--

Peak Autophagy

30h

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Start your fast and let Fasted notify you the moment autophagy begins.

Important disclaimer

Autophagy cannot be measured without specialised laboratory testing. These timelines are based on research averages and are not a diagnosis or medical measurement. Individual results vary significantly. Consult a healthcare professional before undertaking extended fasts.

How this is calculated

One base number and four adjustments. Autophagy is assumed to begin at hour 18 of a fast. A ketogenic or low-carbohydrate last meal moves that 2 hours earlier and a high-carbohydrate one moves it 2 hours later; being active during the fast moves it 1.5 hours earlier and light activity 0.5 hours; being over 50 moves it 1 hour later. The result is clamped to between 16 and 24 hours. Deep autophagy is then set at the onset hour plus 6, and the peak at onset plus 12.

Those adjustments are the ones the mechanism supports, in the directions it supports them: carbohydrate raises insulin and refills glycogen, both of which delay the switch, and exercise burns glycogen off faster. The sizes are this site's judgement, not measurements.

And the honest caveat has to sit above the numbers rather than below them. Autophagy cannot be measured in a living person outside a laboratory. The hours here are estimated from a small literature, much of it in cells and in animals, and nobody has established the fasting duration at which the pathway switches on in a human — never mind to the half hour. Treat the whole page as a considered guess with its reasoning shown, and treat any site that gives you a confident single hour as a site that made one up.

Where this comes from

  1. 1. The Nobel Prize in Physiology or Medicine 2016 — Yoshinori Ohsumi, for discoveries of mechanisms for autophagy — The Nobel Foundation
  2. 2. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting — Anton et al., Obesity, 2018 (PubMed Central)

Nothing on this site is medically reviewed — it cites its sources so you can check them. Read our editorial policy. Method last checked 21 August 2026.

Understanding when autophagy kicks in during your fast is one of the most powerful motivators for extending beyond a standard 16:8 window. This calculator uses research-backed factors to give you a personalised estimate rather than a one-size-fits-all number.

Your last meal composition, activity level, and age all influence how quickly your body depletes glycogen and triggers the cellular recycling process. By adjusting these inputs, you can see how lifestyle choices today affect when autophagy begins tomorrow.

Frequently Asked Questions

How long do you need to fast to trigger autophagy?
Most research suggests autophagy begins around 18-24 hours into a fast for most people. However, the exact timing depends on factors like your last meal composition, activity level, metabolic health, and age. A low-carb last meal and exercise can accelerate onset by several hours.

What is autophagy and why does it matter?
Autophagy is your body's cellular recycling system. During extended fasting, cells break down and repurpose damaged proteins, organelles, and debris. This process supports immune function, reduces inflammation, and may protect against neurodegenerative diseases. Yoshinori Ohsumi won the 2016 Nobel Prize for discovering its mechanisms.

Does exercise speed up autophagy?
Yes. Exercise accelerates glycogen depletion, which is one of the key triggers for autophagy. Studies show that moderate exercise during a fast can bring forward autophagy onset by approximately 1-2 hours compared to remaining sedentary.

Can you measure autophagy at home?
No. Autophagy can only be measured through specialised laboratory tests. The timelines provided by calculators are based on research averages and should be treated as educated estimates. Individual results vary based on metabolic health, body composition, and other factors.

What are the signs you are in autophagy?
There are no definitive external signs of autophagy. Some people report increased mental clarity, reduced hunger (as ketones rise), and a sense of lightness during extended fasts. However, these are indirect indicators and not proof that autophagy is active.

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Start your fast now and let Fasted notify you the moment autophagy begins

The Fasted app tracks your fasting phases in real time and sends you a notification the instant you enter the autophagy zone. Never miss the moment your cells start cleaning up.

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