What is Intermittent Fasting?▼
Intermittent fasting is an eating schedule that alternates between eating and fasting periods. The most common approach is 16:8 — fasting for 16 hours and eating within an 8-hour window. Your daily calorie and macro targets remain the same; only the timing changes.
This calculator distributes your daily macros equally across your meals within the eating window. It also includes an optional eating window optimizer that suggests a specific window start and end time based on your wake time, sleep time, and goals.
How Intermittent Fasting Works
Intermittent fasting (IF) is not a diet in the traditional sense — it does not dictate what you eat, only when. The core principle is simple: all daily eating is compressed into a defined time window, followed by a fasting period. The total daily calories and macros remain the same as any other nutritional plan.
Common IF Protocols
16:8
Most Popular
16 hours fasting, 8-hour eating window. Fits 2–3 meals. Commonly skipping breakfast and eating noon to 8pm.
18:6
Moderate
18 hours fasting, 6-hour eating window. Typically 2 meals. Requires a slightly later eating start (e.g., 2pm to 8pm).
20:4
Strict
20 hours fasting, 4-hour eating window. Often 1–2 large meals. Requires a more disciplined schedule.
Macro Compression
The key concept in this calculator is macro compression: your total daily macros are distributed equally across your eating window meals. If you eat 150g protein per day and plan 2 meals in your 16:8 window, each meal targets 75g protein. This ensures your nutritional goals are met within the eating window regardless of the fasting period.
Choosing Your Eating Window
The eating window optimizer in this calculator uses a schedule-based approach to suggest a practical eating window. For fat loss goals, it delays the window start to extend the morning fast. For muscle gain with an evening workout, it positions the window to include the post-workout period. For general health, it centers the window in your waking hours. These are scheduling suggestions based on your daily routine, not medical recommendations.
What IF Does Not Do
IF does not automatically create a calorie deficit or change your body composition on its own. Body composition changes require appropriate total calories and macros. IF is a timing framework that some people find helps with appetite control and schedule simplicity — it works best when layered on top of a sound nutritional plan rather than used as a standalone approach.
Frequently Asked Questions
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