Periods over your lifetime: Average cycle length by age

What is the average cycle length?

You’ve probably heard it said that 28 days is the average length of the menstrual cycle. But that’s not strictly true. Your menstrual cycle starts on the first day of your period and ends the day before your next period — a length of time that can vary widely from person to person, depending on how often you get your period [1]. 

So, then, what’s normal when it comes to cycle length? Natural Cycles research looked at over 600,000 of our users' cycles and found that just one in eight cycles were 28 days long, and ‘normal’ can be anything between 21 and 35 days [2, 3]. You might also find that different scientific bodies have different classifications for what constitutes a regular cycle, which can be confusing as you work out what your own ‘normal’ is. 

What is a normal period?

Your period marks the start of your menstrual cycle and has its own characteristics that can vary from person to person. A typical period lasts 2 to 7 days [3]. It should be about the same length each cycle, and you usually lose around 20 to 90ml (about 1 to 5 tablespoons) of menstrual blood each period [1]. But again, everybody is different. Some people have heavier periods, some lighter; some have very short periods, and others very long. Just like with the rest of your menstrual cycle, the important thing is to know what is normal for you. 

Although bleeding might vary slightly between cycles (you might bleed for four days one cycle and five the next, for example), you should keep an eye out for any significant changes to the length of your period. Your period length can change because of medical conditions, hormonal birth control, and natural changes as you age — we’ll go into more detail below. Talk to your doctor if you notice changes in your cycle or period so they can check for underlying causes. If you use Natural Cycles, you can download your unique Cycle Report to share with your doctor and help with identifying anything unusual. 

“It’s important to know what a “normal” cycle is, and what are signs of an “abnormal” cycle. I’ve seen countless women with abnormal bleeding, pain or other severe symptoms with periods, missing or irregular periods, who have conditions like endometriosis, adenomyosis, fibroids, PCOS, perimenopause, etc. And obviously if you’re trying to get pregnant, understanding what happens during the parts of the cycle, when ovulation is happening, when intercourse should happen, will optimize your chances of conceiving.” - Dr. Karen Tang, Board-Certified OBGYN & Natural Cycles Medical Advisor

Your period in your 20s: Settling into your cycle

In the US, most girls get their first period at around 12 years of age [4]. During those first few years, your period can be irregular as your hormones settle down, but by your 20s and after puberty has finished, most people’s periods have settled into a more regular rhythm. At this age, our cycles tend to be around 26 to 31 days, though there may still be the occasional irregularity [5, 6].

Your fertility is at its peak between your late teens and late 20s [7]. While it's becoming more and more common to start a family later in life, we think it’s still important to know your fertility at all stages of life. For healthy couples trying to conceive in their 20s and early 30s, around 1 in 4 women will get pregnant in any single menstrual cycle. This declines to around 1 in 10 by age 40 [7]. 

Look out for changes to your cycle

For many people, their 20s are when they notice any unusual symptoms as their cycle settles into a more regular groove. Symptoms of irregular cycles can include:

• A period that lasts longer than seven days
• Periods that are extremely heavy, for example, soaking through one or more tampons per hour
• Cycles that last longer than 35 days or less than 21 days
• Severe pain at any time in your cycle
• Bleeding or spotting between periods
• Pain during or after sex
• Not having a period for three months or longer
• Bleeding after menopause — when you haven’t had your periods for a full year

[3, 8]

Most people will experience the occasional irregularity in their cycles. But if you notice the same symptoms regularly, it may be indicative of a medical condition like PMOS (formerly PCOS) or fibroids. If you notice anything that’s not normal for you, it’s always best to have your healthcare provider check it out.

The impact of birth control on the menstrual cycle

Most combined hormonal birth control works by stopping ovulation from happening [9]. This interrupts your natural menstrual cycle and can mask any unusual symptoms, making it harder to spot irregularities. If you experience a regular bleed while taking it (for example, during a break in taking the pill), this is a withdrawal bleed in response to the hormones from your birth control, rather than a natural period [10]. Other types of hormonal birth control, like the progestin-only mini pill or contraceptive shot, may stop ovulation, but generally use other ways of preventing pregnancy, and can give you irregular bleeding, or no bleeding at all [11]. 

Birth control won’t affect your fertility in the long run, but it is important to be aware of how it can affect your cycle. For contraception that doesn’t affect your cycle, there are non-hormonal options, like condoms, the copper IUD, or Natural Cycles.

If you do have irregular periods or symptoms of conditions like PMOS and endometriosis, sometimes hormonal birth control is prescribed to reduce symptoms such as pain [3]. Both endometriosis and PMOS can affect fertility, so you might not notice that there are any issues until you come off birth control. Many women try out different types of birth control in their 20s, until they find which works best for them.

“Learn the facts about all the contraceptive options from a reliable source...Talk with your gynecologist about your particular situation including your preferences, concerns, anatomy and medical history, risk factors, goals for future fertility, to help determine which method would be the best fit for you.” - Dr. Karen Tang, Board-Certified OBGYN & Natural Cycles Medical Advisor

Your period in your 30s: A mixed experience

In your 30s, your cycle length is likely to be 26 to 29 days, and you might find it is more regular than in your 20s [5]. But you can think of your 30s as a decade of two halves. In your early 30s, fertility is typically much the same as in your 20s, since you’re likely still ovulating regularly.

As you approach your late 30s, fertility starts to decline. Your fertility will continue to decrease each year as your egg count and the number of good-quality eggs decline with age [12]. Your cycle is likely still regular overall, but you might start noticing a few changes, such as a heavier or lighter period, or the appearance of shorter cycles [5]. 

Fertility and pregnancy planning

Of course, it’s important to note that many women manage to successfully conceive at this age. The CDC reported that in 2023, the mean age of women giving birth in the USA was 30, the highest ever on record, and the mean age for giving birth to their first child was 27.5 [13]. It’s a similar story across the pond, with a mean age of 31 in 2020 for women giving birth in England and Wales [14]. 

The good news is your chance of conceiving within the first 12 months of trying is still 75% at age 30, and 66% at age 35 [15]. If you’re planning a pregnancy, Natural Cycles can help you find your fertile days to help you conceive faster — on average, those who plan their pregnancy with Natural Cycles conceive in just three cycles [16].

“I have been learning about my body and supporting my health for a while from various sources and the information on the NC° app and Instagram page complemented that learning and helped me to know my body's cycle and signals really well” - Isabelle, NC° user

Your period and pregnancy

Of course, being pregnant means you won’t get a period for the duration of your pregnancy. It’s worth noting that up to a quarter of women do have some bleeding during early pregnancy — it isn’t always a cause for concern, but it is important to get checked out by your doctor [17]. 

It can take a while for your period to return after you give birth, but for most women, it does come back within a year. A survey of Natural Cycles users who had given birth in the last 6-24 months found that one in four Cyclers got their first period within three months after giving birth, half got their period back within six months, and three in four women got their period back within a year [18]. The survey results also suggested that feeding method — breastfeeding, pumping, or formula-feeding — might affect the return of your period. 90% of respondents who were formula feeding, and 92% who were pumping, had their periods return within the first year, compared to 79% of respondents who were breastfeeding [18]. 

Your period in your 40s: A time for change

In your early 40s, cycles can be more regular than ever, and average 25 to 28 days long. From your mid-40s, they tend to become more irregular, and you might also experience more cycles when you don’t ovulate, called anovulatory cycles [5]. 

It's also common for women to experience the first symptoms of perimenopause — the transitional phase before menopause — in their 40s. During this time, it's common to have very long cycles, especially as menopause approaches. Menopause is technically confirmed when you haven't had a period for a full year. In the US, the average age women reach menopause is 52, but it can happen anytime between the ages of 45 and 55 [8]. It’s rare for menopause to occur before the age of 40, but it does happen for 1 in 100 women. This is known as premature menopause [19]. If you are experiencing perimenopause symptoms, speak to your doctor or healthcare provider for support. 

Perimenopause signs

Remember, everyone experiences perimenopause differently. Some people may have lots of signs, while others may have none. For some people, perimenopause kicks in just months before menopause, while others experience symptoms for years before their periods stop. Some of the most common symptoms of perimenopause are:

• Irregular periods
• Night sweats
• Vaginal dryness
• Hot flashes
• Lower libido
• Mood changes
• Anxiety
• Difficulty sleeping
• Brain fog or problems with memory

[8]

Keep in mind that perimenopause looks different for everyone. If you have any questions about your symptoms or find that they are interfering with your quality of life, it’s important to talk to your doctor.

The effects of birth control on perimenopause

In the same way hormonal birth control can mask cycle irregularities in your 20s and 30s, it can also make it difficult to know when symptoms of perimenopause or menopause begin. But hormonal birth control can also provide symptom relief for some people and help ease the transition. Others choose to use hormone therapy, also known as hormone replacement therapy or HRT, a treatment that delivers similar hormones to birth control, but that is specifically designed to treat perimenopause symptoms and does not provide protection against pregnancy [20].

Not everyone needs medical treatment for perimenopause symptoms, and it's important to choose what's right for you, your lifestyle, and your health. Always speak to your healthcare practitioner before starting any medication or treatment. 

“Treatments [for perimenopause symptoms] like hormone therapy are the most effective when looking at outcomes and studies; antidepressants or lifestyle changes can also be very effective. The best option depends on your symptoms and health risks...If symptoms interfere with daily life or if you're concerned about specific symptoms, it’s a good idea to talk to your doctor for guidance and treatment options.” - Dr. Jessica Shepherd, Board-Certified OBGYN & Natural Cycles Medical Advisor

Pregnancy in your 40s

Even if you start experiencing symptoms of perimenopause in your 40s, you can still get pregnant as long as you’re ovulating. However, as ovulation becomes less frequent, it can be harder to get pregnant. If you are hoping to have a child, you might consider tracking ovulation and patterns in your cycle to better understand the best time to try for a baby each cycle. Starting to track your cycle when you’re younger can help you spot any patterns or issues when you are ready to get pregnant, and you can always speak to your doctor if you have any fertility concerns.

Irregular cycles and bleeding

As we’ve outlined, your cycle may be irregular at different stages of your life. It’s typically most regular in your 20s and 30s, then may become more irregular as you get older and ovulation decreases.

Remember, an occasional irregular cycle or irregular bleeding isn’t always a cause for concern. It’s very common, for example, to have irregular bleeding with some hormonal methods of contraception. Stress can also cause cycle changes from time to time [21]. Though it’s not always something to worry about, tracking your cycle is a good idea to help you spot anything out of the ordinary, and you should always speak to your doctor about any irregularities.

What your period can tell you

Bleeding may vary slightly throughout your life, but your period length should typically stay the same from cycle to cycle. If you notice significant changes in cycle length or irregular bleeding, tell your doctor. These changes can sometimes indicate an underlying condition or the start of a different life phase, like perimenopause.

The color of your period blood can also tell you a lot about the stage of your cycle and whether there are any underlying health concerns. Healthy period blood is typically red at its heaviest, but can be pink or brown on lighter days [22]. Period blood can be different colors for many reasons, for example: 

• Brown blood: You may notice brown discharge or blood near the start or end of your period, when your flow is lighter [22]. It can be perfectly normal, but it can also be a sign of perimenopause, as a result of your periods getting lighter or vaginal dryness [23].
• Pink blood: Withdrawal bleeding or breakthrough bleeding as a result of hormonal birth control can sometimes show as pink bleeding or spotting [9].
• Gray discharge: This can indicate an infection, such as bacterial vaginosis, especially if accompanied by a foul smell [24]. 

Tracking your discharge, period, and menstrual cycle symptoms with Natural Cycles can help you learn more about your cycle and provide powerful information, whether you’re trying to conceive, preventing pregnancy, or simply watching for irregularities.

When to see a doctor

If you notice anything unusual for you, then it’s a good idea to see your doctor. Irregularities could include:

• Periods that last for longer than seven days
• Heavy bleeding, for example, soaking through a tampon or pad every one or two hours
• Menstrual cycles that are shorter than 21 days or longer than 35 days
• Menstrual cycles that vary by more than 7-9 days
• Not having a period for three or more months
• Symptoms of perimenopause or menopause, especially if you are under 40
• Severe pain during your period
• Unusual vaginal discharge
• Bleeding or spotting between periods
• Bleeding or pain during sex

[3, 24]

If you’re tracking your periods, a doctor can use that information to diagnose medical conditions or help you to manage your symptoms. They can also better understand whether you might have any fertility issues, which is especially important if you’re planning a pregnancy.

More than a period tracker

Natural Cycles is more than just a period tracker. It’s the first FDA-cleared app of its kind. Whether you want to learn more about your cycle, are looking for hormone-free contraception, are trying to conceive, or need support through perimenopause, we’re committed to empowering you with insights about your cycle and fertility at all stages of life. 

The NC° app uses your unique cycle data, body temperature, and our specialized algorithm to predict when you'll ovulate, when your period will start, and when you will be fertile each cycle. You can also log symptoms and use your Cycle Report to spot patterns through each cycle phase, making it easier to know what your ‘normal’ is.