You burn roughly 100 to 164 extra calories per day in the days leading up to your period, not during the bleed itself. Researchers at McGill University estimate the variation in basal metabolic rate across the menstrual cycle at about 8 percent, which works out to around 164 calories for an average woman. That bump happens during the luteal phase, the roughly two weeks between ovulation and the start of your period, when progesterone levels are high. Once bleeding actually begins, your metabolism starts dropping back to baseline.
When the Extra Burn Actually Happens
The menstrual cycle has two main halves. The follicular phase starts on day one of your period and lasts until ovulation, around day 14. The luteal phase covers the back half, from ovulation until your next period starts. Your resting metabolic rate climbs during the luteal phase, peaks in the week or so before your period, and then falls once bleeding begins.
This timing surprises most people. The days you feel the worst, with cramps and bloating, are actually when your metabolism is resetting to its lower baseline. The calorie boost was already happening in the week or two before that, when progesterone was elevated and your body was preparing for a potential pregnancy. So the extra burn lines up more with PMS week than with your actual period.
Why Your Body Burns More Before a Period
Progesterone is the main driver. After ovulation, progesterone rises sharply to prepare the uterine lining, and maintaining that preparation takes energy. Your core body temperature increases slightly (often by about half a degree Fahrenheit), which alone requires more fuel. Your body also processes food differently during this phase. One study found that the thermic effect of a meal, the energy your body spends digesting food, jumped by 18.5 percent in the luteal phase compared to the follicular phase.
At the same time, your brain becomes less sensitive to insulin during the luteal phase. Research from the German Center for Diabetes Research found that the brain’s insulin sensitivity is higher in the follicular phase but drops in the luteal phase, contributing to whole-body insulin resistance. This shift can make your body less efficient at using blood sugar for energy, which partly explains why cravings for carbohydrates and fatty foods spike premenstrually.
Why You Feel Hungrier, Not Leaner
If you’re burning an extra 100 to 164 calories a day, you might expect to lose weight. In practice, your body compensates almost perfectly by making you hungrier. Food intake tends to be lowest around ovulation, when estrogen peaks, and highest in the luteal phase, when estrogen drops and progesterone dominates. That pattern isn’t just psychological. The hunger hormone ghrelin becomes more effective at stimulating appetite when estrogen is low. Cravings for high-fat, calorie-dense foods and even binge-eating episodes are more common in the luteal phase as a direct result of these hormonal shifts.
Most women naturally eat enough extra food to offset the metabolic increase, sometimes more. So the extra calorie burn rarely translates into fat loss over a full cycle. Your body is essentially nudging you to eat a bit more to match the higher energy demand.
Water Weight Masks Everything
Even if you didn’t eat a single extra calorie, you likely wouldn’t see the scale budge in your favor. It’s normal to gain three to five pounds of water weight around your period. Hormonal changes cause your body to retain fluid, and that temporary weight gain can easily obscure any subtle fat-burning advantage. The water weight typically drops within a few days of bleeding, which is why many women feel lighter mid-cycle.
If you’re tracking your weight, the most reliable readings come during the mid-follicular phase, roughly days 5 through 10 of your cycle, when both water retention and hormonal fluctuations are at their lowest.
What This Means for Eating and Exercise
The extra 100 to 164 calories is real but modest. It’s roughly equivalent to a banana and a tablespoon of peanut butter. You don’t need to overhaul your diet in the luteal phase, but it does help to know that your increased appetite has a biological basis. Eating slightly more during that window isn’t a failure of willpower; it’s your metabolism asking for fuel it genuinely needs.
For exercise, the luteal phase tends to favor lower-intensity, steady-state activity. Your body is already burning a bit more at rest, and insulin resistance makes it slightly harder to fuel intense efforts with carbohydrates. Many women find that endurance-type workouts feel more natural premenstrually, while the follicular phase, when insulin sensitivity and estrogen are high, is often better suited for high-intensity training and strength work.
None of this is dramatic enough to require a completely different meal plan or workout program for each phase of your cycle. But understanding the pattern can help you stop fighting your body’s signals and recognize that a week of slightly higher hunger and slightly lower energy is a normal metabolic event, not something you need to fix.