Why does my weight go up before my period?

Fluid retention, not fat. Progesterone peaks in the luteal phase — roughly the second half of the cycle — and the body holds more water. The change typically appears 3 to 7 days before a period and resolves 2 to 4 days after bleeding starts. Range varies by person; 0.5 to 3 kg is normal.

How much weight gain is normal before a period?

Most people see between 0.5 and 2 kg of fluid weight in the days before their period. Some see more, some see almost none. The pattern is what matters — consistent rise before, consistent drop after.

Should I stop weighing myself during my luteal phase?

You can. Many people do, and it protects mood on days where the scale reading would otherwise be misleading. An alternative is to keep logging but ignore single-day readings during that window — the long-term trend tells the real story.

Writing · 2026-04-17

Your scale is reading your hormones, not your progress.

Every woman who has ever tracked her weight has seen this: you're doing everything right, and then one morning the scale goes up 1.4 kg overnight. By Wednesday it's back down. By the weekend you've forgotten about it.

This is not a willpower failure. It is not even, really, weight.

In the second half of the menstrual cycle — the luteal phase, running roughly from ovulation to the first day of a period — progesterone peaks. One of the things progesterone does is cause the body to hold more water. The change is mild, usually 0.5 to 2 kg of fluid, and it almost always appears in the 3 to 7 days before bleeding starts. It resolves in the 2 to 4 days after.

The scale, which cannot tell the difference between fluid and fat, reads the fluid as weight. For a person trying to lose weight, this can be genuinely demoralising. The loop is familiar: a rise on the scale, a mood drop, a suspicion that "nothing is working", a resolve to restrict harder. Then the period arrives and the 1.4 kg is gone by Wednesday and the resolve has outlasted its cause by about a week.

The reason it keeps catching people out is that most weight-loss tools were not designed with menstrual cycles in mind. A standard trend line in a weight app treats day 24 the same way it treats day 4. The chart does not know.

You can do two useful things with this information.

The first is to stop weighing yourself in the 5 to 7 days before your period. This is the cleanest solution. If the scale is going to give you information you'll only misread, the information is not worth having. Many people do this and find it protects their mood on exactly the days when their mood is most vulnerable anyway.

The second is to keep weighing yourself, but to stop trusting any single-day reading during that window. Your 90-day trend is the real story. A weight app that knows your cycle can anchor the chart for you — "you are on day 24, of course the number is up, here is the 90-day line" — instead of implying a failure that is not there.

Either works. What does not work is pretending the pattern doesn't exist.

A good health app would know when to be quiet about a single number.

Today is a quiet health partner that correlates your weight, cycle, and mood data — so a scale reading that would have read as failure to a single-domain app reads as "day 24" instead.

Join the beta →

This piece is informational, not medical advice. If something about your cycle, weight, or mood is concerning or out of pattern, talk to a clinician. See our health disclaimer.