Intermittent Fasting Calculator

The 16/8 method involves fasting for 16 consecutive hours and restricting all eating to an 8-hour window each day. For example, you might eat between 12:00 PM and 8:00 PM, then fast until noon the next day. It's the most popular IF protocol because it's easy to maintain long-term — the fasting window largely overlaps with sleep.

Intermittent fasting promotes weight loss primarily by reducing overall calorie intake through restricted eating windows. It also lowers insulin levels during fasting periods, encouraging the body to burn stored fat for energy. Some research suggests IF may also boost metabolic rate slightly and reduce appetite-related hormones like ghrelin.

The 5:2 diet means you eat normally for five days of the week and significantly restrict calories — typically to 500–600 kcal — on two non-consecutive days. This approach is flexible because you choose which two days to fast, making it easier to fit into a social schedule. Your TDEE is used to set the 'normal' eating day targets.

Research suggests intermittent fasting can improve several metabolic markers, including insulin sensitivity, blood sugar levels, blood pressure, and cholesterol profiles. These benefits are largely tied to weight loss, though some studies indicate fasting itself may trigger beneficial cellular repair processes like autophagy independent of calorie reduction.

Staying well-hydrated is the most effective strategy — water, black coffee, and plain tea are all permitted during fasting windows and help suppress appetite. Easing into IF gradually (starting with a 12-hour fast and extending over weeks) also helps your body adapt. Most people report that hunger pangs diminish significantly after the first 1–2 weeks.

Alternate-day fasting involves cycling between regular eating days and fasting days every other day. On fasting days, you either eat nothing or limit intake to about 25% of your TDEE (roughly 500 kcal). It's one of the more aggressive IF protocols and may produce faster weight loss, but can be harder to sustain socially.

The most frequent mistakes include overeating during eating windows to compensate for fasting, choosing an eating window that doesn't align with your lifestyle, not drinking enough water while fasting, and breaking a fast with high-sugar or highly processed foods. Consistency matters most — irregular fasting schedules reduce the metabolic and hormonal benefits.

Most healthy adults can safely practice intermittent fasting, but it's not recommended for pregnant or breastfeeding women, children and teenagers, people with a history of eating disorders, or those with certain medical conditions like type 1 diabetes. Always consult a healthcare provider before starting any IF protocol if you have existing health concerns.