The scale bounces around from day to day. Enter your weigh-ins and this tool draws the trend underneath — a 7-day moving average — and works out your average weekly change, so one high morning doesn’t hide weeks of progress.
Example data. These weigh-ins are made up to show how the tool works. Add your first real one and the example disappears.
Units
Paste a list from a spreadsheet or your notes
One weigh-in per line: the date, then the weight — e.g. 2026-08-03 203.7 or 8/3/2026 203.7 (month/day/year).
Weigh-in (lb)7-day moving average
Latest 7-day average198.5 lbas of Aug 31
Average weekly change−1.31 lb/weekbest-fit line through 26 weigh-ins
The line is a 7-day moving average: for each weigh-in, the average of all your weigh-ins from that day and the six days before it. If you skip days, the window simply holds fewer readings.
The average weekly change is the slope of the straight line that best fits all your weigh-ins (a least-squares fit), multiplied by 7 days. It uses every reading, so one unusual day moves it very little.
7-day average on day d = mean of your weigh-ins from day d−6 to day d
Average weekly change = slope of the best-fit line (per day) × 7
Worked example: weigh-ins of 200.4, 199.2 and 199.8 lb on three days in a row give a 7-day average on the third day of (200.4 + 199.2 + 199.8) ÷ 3 = 199.8 lb. With readings of 202, 201 and 200 lb taken a week apart, the best-fit line falls by 1 lb per week.
Why your weight goes up and down from day to day
Day-to-day changes are mostly water and timing, not body fat. Common reasons:
Salt. A salty meal makes the body hold on to more water for a day or two.
Carbohydrates. Stored carbohydrate (glycogen) is kept with water, so a higher-carb day can show up on the scale.
Timing. Food and drink still in your system, and when you last used the bathroom, change the reading.
Hormones. Many people retain water at certain points of the menstrual cycle.
Exercise. Hard or new workouts can cause temporary water retention while muscles recover.
The calculator shows your own “typical day-to-day move” so you can see how big the noise is for you.
Tips for weigh-ins you can compare
Weigh at the same time of day — many people choose first thing in the morning, after the bathroom and before eating or drinking.
Use the same scale, on a hard, flat floor.
Wear similar clothing (or none) each time.
Weigh as often as suits you: more weigh-ins make the average smoother, but even two or three a week show a trend.
The GLPily app
Let GLPily draw this every day
GLPily keeps every weigh-in, charts your trend by week, month or year with your weekly average and pace to goal, and syncs with Apple Health and Health Connect. Free on iPhone and Android.
Free to download. Pro is an optional subscription for extras like the GLPily Grade for food and unlimited photo scans.
A line that averages out day-to-day ups and downs so you can see the direction your weight is really moving. This tool uses a 7-day moving average.
Why use a 7-day average instead of my daily weight?
Because a single reading can move by more than a week’s worth of real change. Averaging a week of readings cancels out much of the water and timing noise.
Why did my weight jump overnight?
Most overnight jumps are water — a salty or high-carb meal, a late dinner, a hard workout or hormones. If the 7-day average keeps heading the same way, a single jump doesn’t change the picture.
Is my data saved or uploaded?
Nothing is uploaded. Your weigh-ins are saved only in this browser (local storage) so they’re here next time; clearing your browser data or pressing “Delete all” removes them.
Can I paste data from a spreadsheet?
Yes. Open “Paste a list”, put one weigh-in per line — the date, then the weight (for example 2026-08-03 203.7) — and press “Add these weigh-ins”.
Informational only, not medical advice. These calculators do simple arithmetic on the numbers you enter. They don’t diagnose anything and don’t replace your clinician or dietitian. Nothing you type is sent anywhere — it stays in your browser. Updated September 2026.
