BodyCalWhat this intermittent fasting calculator does
Pick a fasting method and the time you want to start eating, and this calculator instantly maps out your day: your exact eating window, your fasting window, when to stop eating, and when to break your fast — all drawn on a simple 24-hour timeline so you can see your schedule at a glance.
The popular fasting methods
- 14:10 — fast 14 hours, eat within 10. The gentlest start and easiest to stick to.
- 16:8 — fast 16, eat within 8. The most popular schedule; usually means skipping breakfast and eating roughly noon to 8pm.
- 18:6 — fast 18, eat within 6. A solid intermediate step.
- 20:4 (Warrior) — fast 20, eat within 4. For those already comfortable with fasting.
- OMAD — one meal a day, a ~23-hour fast. The most demanding; best for experienced fasters.
How intermittent fasting works
For the first several hours after eating, your body runs on glucose. After roughly 12 hours without food it runs low and switches to burning fat for fuel — a process called metabolic switching. This is also when autophagy steps up: your cells clear out damaged components, which research links to lower inflammation and better stress resistance. Practically, most people also simply eat fewer calories with a shorter window, which is why IF tends to support weight loss.
How to start (without hating it)
Ease in. Begin with 14:10 or 16:8 for a couple of weeks before trying anything longer. Push your first meal a little later each day rather than jumping straight to a long fast. Drink plenty of water, black coffee, or plain tea during the fast — they don't break it and they blunt hunger. And when your window opens, eat normally: IF works best when you still get enough protein and nutrients, not when you use it as an excuse to under-eat.
Is it safe for you?
For most healthy adults, intermittent fasting is safe. But it isn't for everyone — avoid it if you're pregnant, breastfeeding, or trying to conceive, under 18, underweight, or have a history of disordered eating, and only fast under medical supervision if you have diabetes or another chronic condition. Fasting is a tool, not a requirement — if it makes you feel unwell or obsessive about food, it's not the right approach for you. Pair it with our calorie deficit calculator and macro calculator to make sure your eating window actually supports your goals, and read our beginner's guide to intermittent fasting.