Why body weight changes from day to day
A scale measures total body mass at that moment. It does not separately identify a change in body fat. Fluid intake and loss, food and drink still being digested, carbohydrate stores, sodium intake, clothing, and the time of measurement can all affect an individual reading.
That is why two consecutive mornings can produce different numbers even when the longer-term direction has not meaningfully changed. The daily entry remains useful evidence; it just should not be asked to tell the entire story by itself.
How a weekly weight average is calculated
Add the recorded weights inside the calendar week, then divide by the number of recorded days. Missing days are not treated as zero.
Recorded weights80.4 + 80.1 + 80.3 + 80.0 + 79.9 kg
Number of entries5
Weekly average80.14 kg
WeekScale also shows the minimum, maximum, date range, number of entries, and change from the most recent earlier week that contains data.
WeekScale groups readings into fixed calendar weeks. For the reasoning behind that choice, see why WeekScale uses calendar weeks.
More readings make the average more representative
An average based on one reading technically exists, but it says little more than that one reading. WeekScale's Reliability Score reports how many of the seven calendar days contain an entry: one day is 14%, five days is 71%, and seven days is 100%.
The score is not a judgment and it does not claim medical certainty. It is a visible reminder of how complete the period is. Weeks with five or more entries receive the app's reliable-week treatment.
Consistency improves comparability
If you choose to weigh regularly, similar conditions make readings easier to compare: roughly the same time of day, similar clothing, the same scale, and a consistent routine. WeekScale records what you enter; it does not attempt to “correct” a reading with an opaque model.
Hydration, nutrition, activity, sleep, medication, health conditions, and many other factors can affect body weight or how it should be interpreted. For general health guidance, use reputable sources such as the NHS Better Health guidance, and speak with a qualified healthcare professional about personal concerns.
Calendar weeks by design
Your week is the unit.
Log daily when it is useful. Compare weekly averages when you want the broader direction.
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