Short answer: weigh yourself first thing in the morning, after the toilet, before you eat or drink anything, on the same scale in the same spot. Do it every day and judge the 7 to 10 day average, not the number. Those five conditions remove most of the 1 to 2 kg that weight moves within a day, so what is left is closer to real change.
These are the rules behind my live weight prediction log. The model learns from every weigh-in, so a reading taken under different conditions does not just add noise. It teaches the model something false. Here is the protocol, and the readings it made me throw out.
My weigh-in protocol
| Rule | Why |
|---|---|
| Morning, on waking | Overnight is the longest stretch without food or drink. Evening weight carries the day’s 1 to 2 kg of food and fluid. |
| Fasted: no food, coffee or water first | A 500 ml drink is 0.5 kg on the scale for the next hour. |
| After the bladder; note the bowels | The bladder is easy to standardise. A bowel movement is not, so I log yes or no with every reading (why). |
| One scale, one spot | Different scales disagree by 0.5 kg or more. Mine is the same scale at the same gym, on a hard floor. |
| Same clothing | None, or the same light kit every time. |
| Every day | More readings make the average steadier. A missed day is fine; a changed condition is not. |
Readings I throw out
Every one of these is still stored, with a note. None of them goes into the trend or grades a prediction.
- After a flight. 92.2 kg on 20 October 2026, the morning after a flight, against 88.0 kg two days later. Dry cabin air, salty plane food and hours of sitting put on water that is gone within two or three days.
- After breakfast or on a gym scale. 26 August: 90.2 kg on a gym scale after breakfast, against 89.3 kg fasted the next morning.
- After food in the night. 1 September: a head cold, up at 02:30, about 400 kcal of cereal, protein and honey before the weigh-in.
- Any reading not flagged fasted. If I cannot remember, it does not count.
How often to weigh yourself
Daily, if you can look past the day. Daily weighing gives the trend seven points a week instead of one, so it settles within a week. Weekly weighing works if daily numbers mess with your head, but one reading a week can sit a kilo above or below the trend (in my log, the morning-to-morning change exceeds 1 kg on about one day in four), so you need a month to see a direction.
The habit that matters more than frequency is what you do with the number. If you would change your eating because of one morning, weigh less often. If you can write it down and wait for the average, weigh daily.
Smart scales: what to trust
- Weight: consistent to about 0.1 kg on a hard floor. Consistency is what you need; absolute accuracy against a doctor’s scale matters less.
- Body fat %: foot-to-foot impedance estimates fat from how fast a small current passes through your legs. It moves with hydration and can be several points off a DEXA. Use it as a slow trend over weeks, never as a daily number.
- Sync, not memory: the best smart-scale feature is that it logs automatically. A reading you forget to write down is a missing day.
Frequently Asked Questions
What is the best time of day to weigh yourself?
First thing in the morning, after using the toilet and before eating or drinking. It is the one moment of the day when food, drinks and the day’s activity are least in play, so readings are comparable from day to day.
How often should you weigh yourself?
Daily, if you look at the 7 to 10 day average rather than the day. Weekly is the alternative if daily numbers affect your mood, but a single weekly reading can be 1 kg off the trend in either direction, so it takes a month to see a direction.
Why do different scales show different weights?
Calibration, floor surface and where you stand on the plate. Two scales can disagree by 0.5 kg or more. Pick one, keep it on a hard floor in the same spot, and do not compare numbers across scales.
Are smart scales accurate for body fat?
For weight, a decent smart scale is consistent to about 0.1 kg. For body fat, foot-to-foot impedance can be several percentage points off a DEXA scan and shifts with hydration, so use the trend over weeks and ignore day-to-day body-fat changes.
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