Fasting Calculator
Enter when you last ate and when you plan to eat next. You will get the length of the fast and an honest account of what may — and may not — be happening along the way.
This calculator is general education, not medical advice, and it does not know anything about you. Fasting is not safe for everyone. If you take any medication that lowers blood sugar — insulin, a sulfonylurea, a GLP-1 — fasting can drop you low, and that risk is real rather than theoretical. The same caution applies if you are pregnant or nursing, are underweight, have a history of disordered eating, or manage any chronic condition. Talk to your own doctor before changing when you eat, and stop and eat if you feel unwell.
Where this comes from
This calculator refuses to promise you anything, and that is deliberate. It comes out of the same approach as the book: measure first, claim less than you can prove, and ask your own doctor.
Read the bookThis calculator is general education, not medical advice, and it does not know anything about you. Fasting is not safe for everyone. If you take any medication that lowers blood sugar — insulin, a sulfonylurea, a GLP-1 — fasting can drop you low, and that risk is real rather than theoretical. The same caution applies if you are pregnant or nursing, are underweight, have a history of disordered eating, or manage any chronic condition. Talk to your own doctor before changing when you eat, and stop and eat if you feel unwell.