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Intermittent Fasting Calculator

Calculate your IF schedule. Choose a protocol and wake-up time — get your exact eating window, fasting period, meal suggestions, and optimal workout timing.

What is intermittent fasting?

Intermittent fasting (IF) is not a diet in the traditional sense — it does not tell you what to eat, only when to eat. Food intake is limited to a specific time window each day, and the rest of the time you fast. The most common approach is 16:8, where you eat within 8 hours and fast for 16 hours.

In practice, many people already do IF without realizing it: if you eat your last meal at 7 PM and your next meal at 8 AM, you've already fasted for 13 hours. Moving to the 16:8 protocol simply means extending that window a little further.

Comparing IF protocols

ProtocolFastEatingDifficulty
🟢 12:1212h12hEasy
⭐ 16:816h8hMost popular
🟡 18:618h6hIntermediate
🟠 20:420h4hAdvanced
🟣 5:22 days/wk5 days/wkVariable

IF and exercise – the best combination

The optimal workout timing with IF is just before the eating window opens. This way you train in a fasted state, which maximizes fat burning, and immediately after the workout your eating window begins — optimizing recovery with protein and carbohydrates.

🌅

Fasted training

Train in a fasted state before the eating window. Maximizes fat burning and EPOC effect.

Fat burning
🍽️

Train at window open

Train as soon as the eating window opens. Good recovery, moderate fat burning.

Balanced
💪

Train mid-window

Train at full energy mid-window. Best performance, muscle building focus.

Muscle gain

Frequently asked questions

Intermittent fasting (IF) is an eating pattern where food intake is restricted to a specific time window each day. The most common approach is 16:8, where you fast for 16 hours and eat within an 8-hour window. IF does not restrict what you eat, only when you eat. Research suggests IF can help with weight management, improve insulin sensitivity, and support cellular renewal.
16:8 is the most popular and easiest for beginners. In practice, it means eating starts at noon and ends at 8 PM, with sleep counting toward the fasting period. Many people already do this without realizing it if they skip late-night snacks and eat a late breakfast. 12:12 is an even gentler way to start and get your body used to fasting.
Yes, light to moderate exercise during a fast is safe and works well for many people. Fat is the primary energy source in a fasted state, which can enhance fat burning. However, intense strength training or long endurance sessions are best done during or just after the eating window to ensure proper recovery. A good strategy is to train just before the eating window opens.
Black coffee without sugar or milk does not practically break a fast — it contains fewer than 5 calories. The same applies to water and unsweetened tea. However, cream coffee, bulletproof coffee, milk, sugar, and sweeteners can break the metabolic fasting state. In practical IF, black coffee is fully allowed during the fasting period.
Research-supported benefits include: weight management (easier calorie deficit), improved insulin sensitivity, increased autophagy (cellular cleanup), lower inflammation markers, and for some people, improved cognitive performance. IF is not a magic solution — benefits come primarily from reduced calorie intake, not from fasting itself.
During short fasts (16–24 hours), muscle loss is minimal, especially if protein intake is adequate during the eating window. Sufficient protein (1.6–2.2 g/kg/day) and resistance training effectively protect muscle mass during IF. Extended fasts or very low protein intake, however, can lead to muscle catabolism.

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