Do boobs get bigger before your period? Experts say yes—here's how to measure bra size during your cycle

Do boobs get bigger before your period? The answer: a resounding yes across the board. Even if you have mastered measuring bra size, you may get different results depending on when you measure, particularly during your cycle.

And more often than not, the best bras on the market can't adapt to our changing boob sizes through the month—not even comfier options, like the best strapless bras and bralettes, or stretchy non-wired bras. The good news is that we’re all in the same boat, but to help us better understand how our bodies work, we’ve enlisted the help of some trusted experts to answer our bust-based questions. 

Why does bra sizing change during my cycle?

Now for the science part. As with the most unusual happenings within the body, a change in bra sizing is largely due to hormonal influences.

“Oestrogen and progesterone both impact the size of your breasts during your cycle,” explains Dr. Anne Henderson, gynecologist and menopause specialist.

“Oestrogen, which is a predominantly female hormone, has a stimulant effect in breast tissue. This accounts for the majority of size fluctuations during the month. It also improves skin elasticity, which can change the overall appearance of breast tissue, boosting your bust with a natural lifting effect.”

Bigger, perkier boobs? So far, so good.

On the other hand, Progesterone can be responsible for some of the more uncomfortable side effects of a change in breast size.

“A rise in progesterone results in an increase in breast size due to fluid retention, but does also tend to cause more pain, discomfort, and tenderness,” explains Dr. Anne.

At what point in my cycle will my boobs be biggest?

“Everyone is different, but I would say typically people notice their breasts become bigger during the premenstrual phase, after ovulation, and before bleeding,” says Claire Baker, period coach and author of 50 Things You Need To Know About Periods.

If you notice a really significant change in your bust during the month, you’re not alone.

“In women who are very sensitive to hormone and insulin fluctuations, breast size can change by as much as a cup size or more during the month,” explains Dr. Anne. “This can be reflected in dress size, too, increasing in the week leading up to your period before returning to your baseline size once again.”

What you eat can also play a part in how you measure bra size for fit.

“A carbohydrate-rich diet has also been known to increase breast size,” continues Dr. Anne. “This is largely due to water retention. Premenstrual cravings mean some women increase their carb intake as their period approaches, which can exacerbate the effect that hormones have on the breast tissue.”

At what point in my cycle should I measure my bra size?

There are no hard-and-fast rules for measuring bra sizing, but for an accurate result, the pros recommend going for a bra fitting around the middle of your cycle.

“You want to measure your bust when your breasts are most settled, which tends to be in the week after your period, and before your fertile window,” says Curvy Kate’s ‘bra whisperer,’ Katie Weir.

If you find your bust is spilling out of your normal bras as your period approaches, it might be worth investing in a new bra, especially for this time of the month.

The type of bra you wear is important, too.

“A bra with stretch lace on the cups is great for the days you need a little more room,” advises Laura Franklin, customer services manager at Bravissimo.

“Your dedicated ‘period bra’ might be a soft cup, or perhaps a size bigger, so you can accommodate the monthly fluctuation without compromising on comfort,” adds Katie.

Good support is more important than ever when your boobs are at their biggest, as this is when the ligaments that keep your breasts perky are under the most strain. It might sound silly, but sports bras are a great choice these days, especially compared to other types of bras. Not only are they comfy enough to wear all day, but they’ll also provide just the support you need.

How else can my boobs change during my cycle?

If a change in size wasn’t enough to contend with, there are other ways your boobs can change during the month, too.

“Lumpiness tends to occur throughout the cycle, and breasts may feel quite uneven and textured,” explains Dr. Anne. “This is largely due to an enlargement of the glandular texture as your body prepares for a potential pregnancy.

“This tends to peak around the same time as your bra sizing increases, towards the end of the month when menstruation begins. Breasts tend to feel painful and tender around this time, too.”

Is it normal to experience breast pain as your bra sizing changes?

“Breast pain, or mastalgia, to use its medical name, is triggered by hormone fluctuations during the monthly cycle,” explains Dr. Anne. “It can be influenced by a range of factors, including the rise and fall of estrogen and progesterone levels, as well as insulin levels (which are influenced by diet).

“By their very nature, breasts are sensitive, and pain is easily triggered owing to the high volume of nerve receptors within the tissue. These exist to help with breastfeeding.”

Thankfully, monthly breast pain is not a cause for concern. In fact, it’s so common that Dr. Anne considers it completely normal.

How can I reduce monthly breast pain?

As with all premenstrual symptoms, breast pain should make itself scarce within a couple of days, with boobs returning to your normal bra sizing by day two of your period.

If taking it easy isn’t enough to alleviate the pain, there are some lifestyle changes you can try.

“Making sure you’re getting a good amount of sleep, drinking lots of water, eating well, and taking care of your gut – these will all reduce breast pain,” says Claire. “There have been some studies that have shown a link between caffeine consumption and breast tenderness within the cycle, too.” So, skipping your morning coffee could be a good place to start.

“Tracking and charting your cycle will help you notice patterns of when you suffer breast pain and swelling, so you can take steps to eradicate the symptoms,” Claire adds.