Deficitly
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Do you gain weight on your period?
Yes, many women weigh 0.5 to 2 kg (1 to 5 lb) more in the days before and at the start of a period. It's almost all water, with some extra food and gut contents, and it's gone within a few days of the period starting. It isn't fat: adding 1 kg of fat takes about 7,700 extra calories, which is 1,100 calories a day more than you burn for a week. At 65 kg (143 lb) and 165 cm, a woman of 30 burns about 1,870 calories a day with 8,000 steps; a few days of PMS don't come close.
How much weight do you gain on your period?
Most women who track it see 0.5 to 2 kg (1 to 5 lb) above their usual weight at the worst point, which is typically the last days before the period or the first day or two of it. Some see nothing, and a few see more. The number depends on how much water you hold, how much you eat, how constipated you are, and how much salt and carbohydrate you had that week.
A fair rule: if the scale is up by 2 kg or less and your period is due or just started, expect it to drop back within about a week. If you're also trying to lose weight, that's the single most common reason for a "stall" (weight-loss plateau).
Why do you gain weight on your period?
- Hormone shifts move water. Oestrogen and progesterone change how your kidneys handle salt and fluid, so more water stays in your tissues in the second half of the cycle and is released when the period starts.
- Bloating and constipation. Slower digestion in the luteal phase means more in the gut, which can add half a kilo or more.
- You eat more. Reviews find that women eat more in the luteal phase and crave carbohydrate- and fat-rich foods more often (Davidsen 2007). See the energy section below.
- Extra carbs and salt. Carbohydrate is stored as glycogen with about 3 to 4 g of water per gram (water weight explained), and salt holds water. A chocolate-and-crisps weekend can add a kilo on the scale by Monday.
- Sore, swollen tissue. Breast tenderness and puffiness add a little, too.
Is it fat?
Almost never. Fat takes a long time to put on. One kilogram needs about 7,700 calories more than you burn, which means:
| Fat gained | In a week | In 3 days |
|---|---|---|
| 0.5 kg 1.1 lb | 550 kcal/day above what you burn | 1,280 kcal/day above what you burn |
| 1 kg 2.2 lb | 1,100 kcal/day above what you burn | 2,570 kcal/day above what you burn |
| 2 kg 4.4 lb | 2,200 kcal/day above what you burn | 5,130 kcal/day above what you burn |
Eating a few hundred calories extra for a few days, as many women do around their period, adds about 100 g of fat at most. The rest of what you see is water and gut contents. The same logic applies to every sudden jump on the scale; see why your weight fluctuates and is the 3,500-calorie rule accurate?
Does your metabolism change before your period?
A little. Energy use is higher in the luteal phase (the two weeks before the period) than in the first half of the cycle. A small calorimetry study of 10 women found 24-hour expenditure about 9% higher after ovulation (Webb 1986); a 2020 meta-analysis of 26 studies found a small rise in resting metabolism, which was no longer statistically significant in the studies published since 2000 (Benton 2020). For a woman of 30, 65 kg (143 lb), 165 cm, the Mifflin-St Jeor resting burn is 1,370 calories a day. A rise of 5% would be about 70 calories a day, or roughly 950 calories over the two luteal weeks. That's about 125 g of fat's worth of energy. It's real but small, and appetite tends to rise by about as much, so it doesn't change the maths of a diet (BMR calculator).
How to weigh yourself across your cycle
If you weigh daily, the scale will show a wave. The fix is to compare like with like:
- Compare the same cycle day month to month, for example the day after your period ends. Fat loss shows up as that number going down.
- Or use 4-week averages (a full cycle). Compare the average of this cycle with the last one.
- Don't judge a diet by the days around your period. Wait for the weight to settle before deciding it isn't working.
| Cycle days | Phase | Average scale reading |
|---|---|---|
| Days 1–3 | period starts | 65.4 kg |
| Days 4–12 | after the period | 64.6 kg |
| Days 13–16 | around ovulation | 64.8 kg |
| Days 17–24 | luteal phase | 65.1 kg |
| Days 25–28 | just before the period | 65.5 kg |
| Whole cycle | average of all 28 days | 65.0 kg |
The "observed" calculator above does the same job over any 28 days: it takes your weight trend and your logged food and returns your real daily burn (how to find your real TDEE). Run it across a full cycle for the cleanest answer.
How to reduce period bloating
- Keep salt reasonable and avoid very salty meals in the days before your period.
- Drink normally. Cutting back on water doesn't reduce water weight.
- Eat fibre and move daily; walking helps digestion and constipation (how many steps a day).
- Keep alcohol low; it adds both water retention and calories.
- Don't swing from strict eating to bingeing. A normal, regular intake keeps the swing smaller.
- Be patient: it goes by itself within days. Diuretics and "detox" teas don't change fat.
Menopause brings its own weight changes: see menopause weight gain. More on stalls with a deficit: calorie deficit but not losing weight.
When to see a doctor
See a doctor if you gain weight quickly (more than 2 kg in a week) without a clear reason, if the gain doesn't go after your period, if your periods are irregular or have stopped, or if you also have heavy bleeding, pain, hair growth, acne, fatigue, feeling cold or swelling of your legs or face. Polycystic ovary syndrome (PCOS), an underactive thyroid and some medicines can cause weight gain that doesn't come off by itself. Severe PMS with low mood (PMDD) is treatable.
How many calories to eat in general: how many calories should a woman eat.
Sources
- Davidsen L, Vistisen B, Astrup A. Impact of the menstrual cycle on determinants of energy balance: a putative role in weight loss attempts. Int J Obes 2007;31(12):1777–1785.
- Benton MJ, Hutchins AM, Dawes JJ. Effect of menstrual cycle on resting metabolism: a systematic review and meta-analysis. PLoS One 2020;15(7):e0236025.
- Webb P. 24-hour energy expenditure and the menstrual cycle. Am J Clin Nutr 1986;44(5):614–619.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378(9793):826–837.