5:2 Diet Calculator

Unlike a daily eating window, 5:2 works on a weekly ledger rather than an everyday one. Five days you eat at maintenance, and two days you drop to a small allowance, so the deficit comes from those two days averaged across the whole week. For the worked body — maintenance about 1,990 calories — the sum is straightforward: five days at 1,990 is 9,950 calories, plus two fast days at 500 is 1,000, for a weekly total near 10,935. Divide by seven and the average daily intake is about 1,560 calories, which is roughly a 425-calorie daily deficit even though you never restrict on five of the seven days. That weekly framing is what makes 5:2 feel manageable to people who dislike counting every day, and it is exactly how the calculator above tallies your own numbers.

A 425-calorie average daily deficit is about 2,975 calories a week, which at roughly 7,700 calories per kilo of fat comes to about 0.39 kg — near 0.85 lb — every week for the worked body. That is a touch gentler than a daily 16:8 window, and deliberately so: because five days of the week carry no restriction, the fast days do all the work but only twice. For many people that trade — two harder days in exchange for five easy ones — is far easier to sustain than a constant deficit, and sustainability is what actually determines results over months. Confirm the maintenance the estimate rests on with the BMR Calculator, then read your weekly range above.

Choosing Your Fast-Day Calories

The classic 5:2 allowance is 500 calories for women and 600 for men, and that is what this calculator assumes — but the number is a lever, not a law. Set the fast-day allowance lower and the weekly deficit grows; set it higher and the days are easier but the loss slows. What matters most is honesty about the five normal days: if they drift above maintenance, they quietly erase the deficit the two fast days created. The tool lets you enter your own fast-day figure so the projection matches the plan you'll actually follow.

A whole-day plan like 5:2 and a daily eating window like 16:8 can produce the same weekly deficit — they just shape it differently. 5:2 concentrates the restriction into two tougher days and leaves the rest of the week free; a daily window spreads a smaller, constant cut across every day. Neither is metabolically superior, and controlled research finds fasting patterns work through the calorie deficit they create rather than any special mechanism (Liu et al., NEJM 2022). Pick the shape that suits your temperament: if you would rather have most days normal, 5:2 fits; if you prefer a steady daily rhythm, plan it with the Calorie Deficit Calculator.