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About this tool
Work out calorie, protein, fat and carbohydrate targets for a planned refeed day, plus what it costs your weekly deficit.
A refeed day is a planned day at or slightly above maintenance calories where the extra energy comes almost entirely from carbohydrate. This calculator derives maintenance from the Mifflin-St Jeor equation plus an activity multiplier, holds protein constant, drops fat to a floor around 0.5 g per kg, and gives carbohydrate the remaining calories using the Atwater factors of 4, 4 and 9 kcal per gram. It also shows the weekly deficit before and after the refeed, so you can see exactly what the day costs in fat loss.
Open Refeed Day Calculator on AltFTool — it loads instantly in your browser.
Enter sex, age, height (cm), body weight (kg), activity level and your Normal diet-day calories (kcal), then set Protein (g per kg body weight) and Refeed-day fat (g per kg body weight).
Pick a Refeed level and Refeed days per week (1, 2 or 3); maintenance comes from Mifflin-St Jeor plus the activity multiplier, protein stays fixed, fat drops to its floor and carbohydrate takes the remaining calories at 4 kcal per gram.
Read the refeed-day carbohydrate figure in grams, the 'Diet day vs refeed day' macro table, the 'What it costs the week' deficit maths and the upper-bound scale rise, then press 'Copy result'.
Protein stays fixed and fat drops to a floor, so the extra calories land where a refeed is supposed to put them.
Shows the kilograms per week given up by adding refeed days, instead of leaving you to guess.
Gives an upper-bound water-weight figure from roughly 3 g of water per gram of stored glycogen.
Enough to fill the calorie target once protein and fat are set — typically 4-7 g per kg of body weight, which is around 350-550 g for an 80 kg person at maintenance. The exact figure depends on your maintenance calories and how low you push fat that day.
A refeed has a calorie ceiling (usually maintenance to maintenance +20%) and a deliberate macro split weighted towards carbohydrate. A cheat day has neither, and can easily run 2,000-3,000 kcal over maintenance — enough to erase a week of deficit.
Stored glycogen holds roughly 3 g of water per gram, so replenishing a few hundred grams of glycogen adds close to a kilogram on the scale overnight. It is water and stored fuel, not fat, and it comes back off over the following days once you return to the diet-day intake.
Practical guidance ties frequency to how lean you are: around twice a week under 10% body fat for men or 18% for women, once a week in the mid range, and once every one to two weeks at higher body fat. This is a training-community heuristic rather than a clinical standard, so treat it as a starting point and discuss any structured diet with a dietitian.
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