Health & Fitness

Intermittent Fasting Calculator | Eating Window, Protocols & Calorie Target

Set your intermittent fasting protocol (16:8, 18:6, 20:4, OMAD, 5:2, Warrior Diet), enter your eating window start time, and get exact eating/fasting start and end times plus a daily calorie target based on your TDEE and weight goal. Includes electrolyte guidance.

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Select Fasting Protocol

Fasting Starts At

Usually after last meal

Eating Window Preview

12:00 – 20:00

8h eating window

Weight

Height

ft / in

Age

Sex

Activity Level

Goal

How Intermittent Fasting Works

Intermittent fasting (IF) is an eating pattern — not a diet — that cycles between periods of fasting and eating. During the fasting window, insulin levels drop, glycogen stores deplete, and the body shifts to burning stored fat for energy. After 12–16 hours of fasting, autophagy (cellular cleanup) also increases.

Comparing IF Protocols

Protocol	Fasting Period	Best For
16:8	16 hours	Beginners, daily adherence, body recomposition
18:6	18 hours	Intermediate — stronger fat loss stimulus
20:4 / Warrior	20 hours	Advanced — one main meal at night
OMAD (23:1)	23 hours	Aggressive fat loss, experienced fasters only
5:2	2 low-cal days/wk	Those who prefer weekly flexibility

What Breaks a Fast?

Plain water, black coffee, plain tea, and sparkling water do not break a fast. Any calories — including those in cream, milk, sweeteners, or bulletproof coffee — technically break the metabolic fast. Even small amounts of protein or fat can trigger an insulin response and stop fat oxidation.

Medical Disclaimer: Intermittent fasting is not appropriate for pregnant women, children, type 1 diabetics, those with a history of eating disorders, or people on certain medications (especially insulin or blood pressure drugs). Always consult a doctor before starting any fasting protocol.

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