The average woman will get 450 periods in her lifetime and, like snowflakes, no two are alike. Everything from diet and exercise to pregnancy and hormonal contraceptives can have an impact on your menstrual cycle, explains women’s health and functional nutrition coach Nicole Jardim.

But those aren’t the only factors that are to blame for a changing cycle — your period actually goes through four distinct stages throughout your life. “There is puberty that brings on a girl’s first period, and includes the teenage years. Then there is the adult menstruation stage, which is followed by perimenopause and then menopause,” explains Jardim. “Each of these stages brings about varying hormonal fluctuations and accompanying symptoms.” Here’s what to expect:

In your teens:
Hello, puberty! Some girls start menstruating as early as nine years old, and others as late as 15, but the median age is between 12 and 13 years old, according to the American College of Obstetricians and Gynecologists. Unfortunately, there’s no easing into it. “Most teenagers have a heavy flow when they first get their periods because of higher estrogen,” says Jardim. That usually regulates as you get older, but expect cycles during the first few years of menstruation to last 21-45 days, and level off at 21-35 days within three years of the first period.

In your 20s:
We’ve got good news and bad news. The good news: as you enter the adult menstruation stage, your hormone levels stabilize, giving you lighter, more regular periods. Beware though, stress levels are at an all-time high now (adults ages 18 to 33 report the highest average level of stress compared to other age groups), which can cause shorter cycles. You may also be experiencing hellish menstrual cramps right about now, thanks to prostaglandins, the hormones your body produces to stimulate contractions and cause the lining of your uterus to shed. Your body produces more of them now (and sometimes as early as your teens), so more painful cramping is normal, but if your cramps are so bad that they get in the way of normal functioning, see a doc. Endometriosis — often under-diagnosed in teens and younger women — or fibroids could be the culprit.

In your 30s:
If you’ve given birth recently — the percentage of women having their first child between ages 30 and 34 was 21% in 2014 (up from 16.5% in 2000), and 9.1% were 35 or older — you may have noticed that your periods have gotten heavier. As Jardim explains, giving birth essentially resets the hormones. “Because women in the postpartum phase haven’t ovulated for a long time, they may be more estrogen dominant and have lower progesterone, which causes heavier periods,” Jardim says. “Some women experience low thyroid function postpartum as well, which can cause the heavier flow.” Irregular and heavy periods are common after miscarriage, too.

In your 40s:
Most women hit menopause between ages 40 and 58, but the average age is 51, which means you’re likely experiencing perimenopause — aka the transition into menopause — in your early- and mid-40s. Even if you didn’t experience heavier or irregular periods after giving birth (or if you haven’t given birth), you may start to now as your progesterone levels drop, causing estrogen to become dominant and interfering with ovulation. Expect a preview of menopause symptoms too, like weight gain, night sweats, sleep problems, low energy, and hot flashes. Keep in mind that thyroid disorders share some symptoms with perimenopause, though, so bring up any concerns to your doctor and don’t skip your regular checkups.

In your 50s:
After 12 months of no menstrual cycle, you’re officially considered menopausal. Sorry, there’s no trophy — just more hot flashes, mood changes, and sleep disturbances. Don’t panic if your hot flashes persist into your 60s: 40% of women 60 to 65 years old still have them, according to a 2015 study. The silver lining? Hormonal therapy is safer and more effective than ever, as long as you start treatment at or near menopause.

Important to remember at any age: if you’re concerned about your cycle, ask your doctor if what you’re experiencing is normal — whether you’re 15, 35, or 55. Period.

Diana Vilibert is a freelance writer and copywriter living in Brooklyn, NY. She loves flea markets, martinis, to-do lists, traveling, and wearing leggings as pants. You can see more of her writing at www.dianavilibert.com and follow her on Twitter at @dianavilibert.