Work out water weight fluctuation instantly with clear inputs, formula shown and shareable results.
Scale weight swings mostly through water, not fat. Each gram of stored glycogen binds about three grams of water, and each extra gram of sodium holds roughly 150 ml. A 200 g carbohydrate increase plus 2 g more sodium can add about 0.9 kg overnight - which is why daily weigh-ins need a weekly average to be meaningful.
Glycogen water
water = carbohydrate stored x 3 g of water per gram
Sodium water
about 150 ml retained per extra gram of sodium
These figures are population-average estimates, not a medical assessment or diagnosis. Body composition equations carry errors of several percentage points, and healthy ranges vary with age, ethnicity, muscularity and medical history. Discuss weight or body composition goals with a qualified clinician or dietitian.
Almost certainly water and gut contents. Gaining a kilogram of fat requires a 7700 kcal surplus, which is not achievable in one meal.
Same time each morning after the toilet, and judge the seven-day rolling average rather than day-to-day changes.