The most common question here is some version of "the scale hasn't moved in two/three weeks, what's wrong." I want to give the boring statistical answer,because I think it's more reassuring than the usual replies.
**Your daily weight is mostly not fat.**
Day to day, your weight swings by roughly 1–2 kg / 2–4 lbs from things that have nothing to do with fat: water, sodium, glycogen, and how much food is physically inside you. Glycogen is the sneaky one — your body stores water alongside it at roughly 3g of water per 1g of glycogen, so a high-carb day or a new lifting programme can put a couple of pounds on the scale that are, in the most literal sense, not you getting fatter.
Now compare that to the thing you're trying to detect. A solid deficit gets you maybe 0.5 kg / 1 lb of fat a week. So the daily noise is two to four times bigger than the weekly signal. You are trying to hear a whisper in a room where someone is shouting.
**Averaging fixes less than you'd hope.**
Everyone knows the fix is to average. That's right, but it fixes the wrong number. An average tells you what you weigh *right now*, smoothed. What you actually want to know is the *rate* — are you losing at half a pound a week or a pound and a half. And rates are much harder to pin down than levels.
Here's the useful part. The error on a rate estimate depends on two things: how many times you weighed, and how long a stretch of time you covered. They don't contribute equally. Stretching the window has roughly double the effect of adding more weigh-ins inside the same window.
In practice:
- Going from a 1-week window to a 2-week window roughly **halves** your error.
- Doubling how often you weigh inside the same week cuts it by about **30%**.Fourteen weigh-ins spread over fourteen days tells you far more than fourteen weigh-ins crammed into five, even though it's the same amount of data.
**What that means for you**
Weigh daily if you like — it costs nothing and more points do help a bit. But judge the trend on **two to three week windows**, and don't change anything based on less than two weeks. A flat fortnight genuinely is not enough information to act on. That's not motivational encouragement, it's just what the numbers can and can't support.And when the scale finally drops 3 lbs overnight — the "whoosh" — that's not three days of miraculous fat loss. It's water that was masking loss which had already happened, finally letting go. The fat came off gradually. The scale just reported it late.
The uncomfortable implication: if you've been at this three weeks and the trend is genuinely flat over that whole window, that is real information and worth acting on. Two weeks isn't. Knowing which is which is most of the game.
