How to use it
Weigh yourself at roughly the same time each day, ideally in the morning after the bathroom. Paste the numbers in order, or paste dates with weights if you skipped days. The calculator averages several weigh-ins on the same day and fills gaps between days in a straight line.
What is trend weight?
Your weight on any single morning includes water, salt, stored carbohydrate and food that hasn't been digested yet. These can move the scale by a kilo or more from one day to the next. Trend weight is an average that smooths those swings out, so the slower change in body fat shows through.
This calculator uses double exponential smoothing: each day's trend is 15% of today's weight and 85% of where the trend was heading, and it keeps track of the slope so the line doesn't lag behind a steady loss or gain.
Trend weight vs weekly average
A 7-day average is the simplest smoothing: add up a week of weigh-ins and divide by seven. It's easy to understand but jumps when a heavy day enters or leaves the window. The smoothed trend changes more gradually and reacts to new direction a little sooner. The weekly rate here is the change in trend over the last two weeks, scaled to seven days.
Why your scale weight jumps around
A salty meal, a carb-heavy dinner, a hard workout or the menstrual cycle can all add water weight for a few days. That's why two single weigh-ins can make a steady loss look like a gain. Give a trend two to four weeks before deciding something has changed.
Frequently asked questions
How many weigh-ins do I need for a useful trend?
The calculator works from three, but a trend becomes meaningful after about two weeks of regular weigh-ins. Four weeks is better for judging your weekly rate.
Is the trend the same as a moving average?
It's a kind of moving average. A simple moving average weights the last seven days equally; the smoothed trend weights recent days more and corrects for lag when your weight is steadily changing.
Why is my trend higher than today's weight?
Because the trend includes the last few days too. If you've had a low day, the trend sits above it; if your weight keeps falling, the trend follows within a few days.
Do you store the numbers I paste?
No. The calculation runs in your browser and nothing is sent to a server or saved.
Sources
- NIST/SEMATECH e-Handbook: double exponential smoothing
- Orsama et al. 2014, weekly weight rhythm (Obesity Facts)
- Kreitzman et al. 1992, glycogen and water (Am J Clin Nutr)
General information, not medical advice.