Intermittent Fasting Calculator

How does intermittent fasting scheduling work?

Intermittent fasting is not about what you eat but when. You split the day into an eating window and a fasting window. A 16:8 plan, the most popular, means 16 hours fasting and an 8 hour eating window. This calculator takes the protocol you pick and the time of your first meal, then works out exactly when your window opens and closes and how long you fast until the next one.

The common protocols

16:8 gives an 8 hour eating window and suits most people as a sustainable starting point. 18:6 tightens it to 6 hours, 20:4 to 4 hours, and OMAD, one meal a day, compresses eating into roughly a single hour. Stricter windows are not automatically better; the right one is the one you can keep up without white-knuckling through your day.

Does fasting itself burn fat?

Fasting can help with weight loss mainly because a shorter eating window naturally trims how much you eat, but the loss itself still comes from a calorie deficit. Pair your schedule with a sensible target from the calorie deficit calculator and a solid protein intake from the protein calculator so the weight you lose is mostly fat. The water intake calculator can set your fluid target, and during your eating window the macro calculator helps you make those meals count.

Who should not fast?

Fasting does not suit everyone. People who are pregnant, have a history of disordered eating, have diabetes on medication, or take medicine that must be taken with food should speak to a doctor first. This is general educational guidance, covered further in our disclaimer.

Choosing a fasting window and protocol

The right schedule is the one that fits your day, so this eating window calculator lets you test each option before committing. A 16:8 fasting schedule is the usual starting point for weight loss because the eight-hour window is easy to keep. An 18:6 fasting plan tightens it further, and OMAD compresses eating into roughly one hour, which suits some people but makes hitting protein and total calories harder. Whatever the fasting hours, move your first meal earlier if a late window disturbs sleep, and let the schedule serve your calorie target rather than replace it.

Limitations of this calculator

This tool builds a schedule of clock times; it does not track what or how much you eat, and it cannot make weight loss happen on its own, since that still depends on a calorie deficit. Individual responses to fasting vary, and longer windows are not inherently better. Fasting is not appropriate during pregnancy, for people with diabetes on medication, or for anyone with a history of disordered eating without medical guidance. Use the schedule as a structure and pair it with a sensible eating target.