Not medical advice
Free Fasting Calculator calculates fasting and eating windows, timers, and schedule options from times you provide. It is provided for informational and scheduling purposes only. Nothing on this site is medical advice, diagnosis, or treatment, and no output of any calculator should be read as a recommendation that fasting, or any particular fasting schedule, is appropriate or safe for you personally.
Talk to a professional if fasting may be complicated for you
Fasting can be medically significant. In particular, consult a qualified healthcare professional before fasting if you have diabetes or take medication that affects blood glucose, are pregnant or breastfeeding, are under 18, have a current or past eating disorder, or have any other medical condition or take any medication where meal timing matters. Stop fasting and seek appropriate care if you feel unwell.
What our numbers mean (and don't)
Our calculators produce arithmetic, not physiology. We deliberately do not display hour-by-hour claims about autophagy, ketosis, "fat-burning stages", or predicted weight loss, because current human evidence does not support assigning such transitions to precise clock times for a given individual. Where our pages discuss research, they aim to describe what studies actually found, including uncertainty.
Use at your own discretion
The site is provided "as is", free of charge, without warranties of any kind. You are responsible for decisions you make based on its output. To the maximum extent permitted by law, the operator is not liable for damages arising from use of the site.
Accuracy of your own inputs
Calculations are only as accurate as the times you enter, and locally stored data can be lost if your browser storage is cleared, so export backups from thehistory page if your records matter to you.