Intermittent Fasting Calculator
How it works
We take your goal-adjusted daily calories, then redistribute the weekly budget: fasting days are capped at about 25% of your daily target (with a floor of ~500 kcal for women, ~600 for men), and the rest is spread across your normal days.
You get both the 5:2 schedule (2 fasting days) and 4:3 (3 fasting days). This models whole-day protocols — not intra-day windows like 16:8.
Frequently asked questions
How many calories should I eat on a fasting day?+
On 5:2 and 4:3 protocols, fasting days are capped at about 25% of your daily calorie target, with a floor of roughly 500 calories for women and 600 for men. This calculator works out both your fasting-day and normal-day calories.
What's the difference between 5:2 and 4:3 fasting?+
5:2 means five normal-eating days and two fasting days each week; 4:3 means four normal and three fasting. Because 4:3 has fewer normal days, those days carry more calories to keep your weekly total the same.
Does intermittent fasting help you lose weight?+
It can, mainly because it's a structured way to eat fewer calories overall. Evidence is mixed and results vary — what matters most is your total weekly calories, which this calculator keeps aligned to your goal.
Does this cover 16:8 or one-meal-a-day?+
No — this tool models whole-day fasting protocols (5:2 and 4:3). Time-restricted eating like 16:8 splits calories within a single day rather than across the week.