Intermittent Fasting Window Calculator

About this calculator

Intermittent fasting protocols such as 16:8, 18:6, 20:4, and one-meal-a-day (OMAD) all work the same way: they compress food intake into a fixed eating window and leave the remaining hours as a fast. The idea builds on time-restricted feeding (TRF) research from circadian-biology labs — Salk Institute researcher Dr. Satchin Panda's studies showed that confining food intake to a consistent daily window can shift metabolic markers independent of calorie changes, which is part of why clock-based fasting schedules spread from bodybuilding circles into mainstream apps like Zero and Life Fasting Tracker.

Turning a protocol label like “16:8” into an actual daily routine means doing the same arithmetic every day: pick a start time for the first meal, then work out when the eating window closes and when the next fast begins. This calculator does that conversion instantly from your first-meal time and target fasting length, so you get concrete clock times to plan meals around work hours, gym sessions, or family dinners instead of counting backward in your head.

It performs only the time arithmetic behind a chosen schedule — it does not judge which fasting length or eating pattern is right for any individual.