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Period Calculator: When Will I Get My Period?

Cycle tracking with an accurate period calculator can help you better understand your body and your health. Learn the benefits of using a period calculator and try it for free on WomanLog!

Period Calculator - Visual representation of a tool to estimate menstrual cycles, ovulation, and fertility for reproductive planning
First day of your last menstrual period
How long did it last (days)?
Your average cycle length (days)
How long did it last (days)?
Your average cycle length (days)

Your menstrual cycle is more than just your period, it is intertwined with countless complex processes throughout your entire body. Using a period calculator is an excellent way to become more aware of your cycle and how your body changes in the different phases. A period calculator can help you get to know your menstrual cycle so you can make the best possible decisions for yourself.


Period Tracker & Calendar

You can track your period using WomanLog. Download WomanLog now:
You can track your period using WomanLog. Download WomanLog now:

The WomanLog period calculator can predict the approximate start date for your next period and when you will ovulate. The longer you use it, the more accurate it will be. If your cycle is irregular, predicting exact dates is more challenging, but as you track what happens over time, you’ll have a much better idea of what to expect. In this article, we answer the most common questions about menstruation, including: When will my period start? How long does a period normally last? Why is my period late? And how does a period tracker work?

When is my period due?

While the average menstrual cycle length is 28 days but anything from 21 to 35 days is considered normal. Some women have very regular, predictable cycles, while others experience some variation in how long each cycle lasts. Irregular periods are especially common in the first few years after puberty begins.

However, if your cycle varies by 7–9 days each month, there’s a good chance something else is going on. Maybe you are under a lot of stress, your body is dealing with an illness, or you have a condition such as polycystic ovary syndrome (PCOS). PCOS affects 4–20% of reproductive-age women worldwide. Symptoms include ovarian cysts, increased sebum production, hirsutism (excessive growth of dark hair on the face, chest, and elsewhere), weight gain, insulin resistance, and irregular or absent periods.

How can I know when my period will come?

The best way to predict when your period will start is to track your cycle month-by-month. Recording when your period starts and how long it lasts will help you understand the rhythm of your cycle, even if it fluctuates.

Your menstrual cycle influences your whole body. As hormone levels shift and the cycle progresses through the four stages of the cycle—menstruation, the follicular phase, ovulation, and the luteal phase—changes take place throughout your body as well.

The cycle starts with menstruation—hormone levels are low, and you are bleeding. In the follicular phase oestrogen levels rise, stimulating a few ovarian follicles to develop and the uterine lining, or endometrium, grows thicker in preparation to receive a fertilised egg. At ovulation, a follicle bursts and a mature egg makes its way through the fallopian tubes to the uterus. If you want to get pregnant, this is your chance. Finally, in the luteal phase, progesterone stops the endometrium from developing and the body prepares to begin another cycle.

By noting changes in your mood, energy levels, and the physical symptoms you experience throughout your cycle, especially before and during your period, you will become more aware of your body. It will be easier to tell when your period is about to start and to notice signs of illness, pregnancy, and other changes.

Recognising 'Signs Your Period is Coming - Visual guide to common premenstrual indicators for menstrual cycle awareness

Signs your period is on the way

Changes in vaginal discharge

After your period, there is usually little to no discharge for a few days, and when it appears it is clear and watery. The amount of discharge will increase gradually throughout the follicular phase. As ovulation approaches, vaginal discharge is abundant and slippery, resembling raw egg whites, to give your body the best chance of getting pregnant. The texture changes again in the luteal phase, becoming thicker and stickier. When you notice this, your period will begin again before too long.

Low energy

Feeling tired and sluggish in the luteal phase before your period is normal. There are several reasons for this:

  • Low oestrogen leads to low mood and low energy.
  • Elevated progesterone leads to increased body temperature which can cause sleep disturbances. Some women find it more difficult to fall asleep and stay asleep during the luteal phase, and some have more nightmares.
  • Preparing for menstruation requires energy and nutrients, which your body may divert from other systems if there isn’t enough to go around. Be sure to eat a healthy and balanced diet to support your body’s needs during this time and throughout the cycle.

Mood changes

Oestrogen and serotonin have been shown to have significant functional interactions, which we are still learning about. Serotonin influences oestrogen synthesis, and oestrogen has serotonin-modulating properties. Serotonin is an important neurotransmitter that regulates mood, sleep, and cognitive function. When oestrogen levels are low in the luteal phase before a new period starts you may also have less serotonin and tend to feel more sensitive and irritable. Many women experience more anxiety, sadness, numbness, apathy, and irritability during this phase of the cycle. When symptoms are severe, we call it PMS.


Abdominal cramps typically begin the same day your period starts, or a few days before, and last for 2 to 3 days. These cramps are caused by the flood of prostaglandins being released from the uterine lining as it prepares to be shed. Prostaglandins stimulate the uterus to contract and expel menstrual blood, but they can also cause abdominal pain and other uncomfortable symptoms like bloating, diarrhoea, and nausea.

Tender breasts

All women experience some degree of cyclical breast swelling and tenderness as their hormones fluctuate. Some women hardly notice, but for others, symptoms can be severe—especially mid-cycle when oestrogen peaks causing the breast ducts to enlarge, and around day 21 (in an average-length cycle) when progesterone peaks causing the lobules (milk glands) to swell.

Oily skin and hair

When your period starts, oestrogen and progesterone levels are low, your skin and hair will tend to be dry, and you may be puffy and bloated from PMS. As your period ends, oestrogen rises and boosts collagen production, and your skin starts looking healthier. Hormone levels peak around ovulation, you feel sexy and energetic, and your skin and hair look great! After ovulation, however, an increase in progesterone raises your body temperature and triggers your sebaceous glands to secrete more sebum—this is an important natural protective lubricant, but it can also cause clogged pores, acne, and oily hair.

Duration of Menstrual Periods - Visual guide providing insights into the typical length and considerations for managing menstrual cycles

How long should a period last?

A menstrual period typically lasts 3–7 days, changing in abundance and colour. Periods tend to become shorter and more regular as we age.  Women have different bodies and different life circumstances, so there is a broad range of “normal”. Tracking your period can help you understand what is normal for you.

When does menstruation stop?

On average, a woman will experience 450–80 menstrual cycles over approximately 40 potentially reproductive years, most commonly between the ages of 12 and 51. Menstruation begins with puberty, which can start as early as age 8 or as late as age 15, and ends with menopause, which can start as early as 40 or as late as 58. During the reproductive years, a woman may stop having her period for various reasons including using hormonal contraception, pregnancy, stress, illness, and dramatic lifestyle changes.

Why is my period late or irregular?

Tracking your cycle can help you notice if your period is late or irregular. It’s important to spot these changes because they can indicate pregnancy or an endocrine issue that requires immediate medical attention.

Reasons for a missed period

  • Using hormonal contraception: Some types of hormonal birth control stop monthly bleeding altogether, while others make your periods shorter and less frequent. Both combination oestrogen/progesterone pills and vaginal rings will stop periods altogether if used continuously. Keeping to a three-weeks-on, one-week-off schedule will ensure you have a regular period during the off week. Women who choose the hormonal intrauterine device (IUD) have a 20–50% chance of period cessation, although they may still experience spotting or irregular bleeding.
  • Pregnancy and breastfeeding: When a fertilized egg implants in the uterus, it begins to secrete human chorionic gonadotrophin (hCG), signalling pregnancy. Implantation can cause some light spotting and cramping, but the endometrial lining—which is usually shed monthly as menstrual blood—turns into the placenta that supplies the baby with oxygen and nutrients. If you are sexually active, it’s important to keep track of your period days and the symptoms you experience because a missed period can indicate pregnancy. After giving birth your period will return within a few weeks or months, but it can take longer for women who breastfeed.
  • PCOS: One of the main symptoms of PCOS is irregular periods. This is caused by unusually high levels of androgens, which can suppress ovulation and throw off your cycle. People with PCOS often have fewer and longer periods.
  • Stress: Lasting stress or big life changes can cause you to miss a period. When you are under stress, your adrenal glands secrete cortisol. This hormone affects every system in your body to maximize your ability to deal with danger. The body is designed to respond to short-term spikes in cortisol, but chronic stress can disrupt oestrogen production, stopping or delaying ovulation and menstruation.
  • Not eating enough: The production of luteinizing hormone (LH)—the hormone that triggers ovulation—partially depends on available calories. Drastically restricting calories can hinder ovulation and disrupt the menstrual cycle.

How to track a period with the WomanLog period calculator?

The WomanLog period calculator is a free tool that helps you predict the start date for your next period and your fertility window, and helps you track symptoms to understand your body better. The calculator uses the information you provide to make predictions. The more information it has, the better the predictions will be. When you have entered information for six cycles, you will start to recognize tendencies and have fairly accurate forecasts about what to expect. Download our free period tracking app and try it for yourself!

What are the benefits of the WomanLog period calculator?

Better understanding of your body

Without tracking, it can be difficult to notice repeated symptoms or patterns of your cycle. With the accurate period tracker, you can follow the dates and symptoms of your cycle to know what to expect next. Our period tracker can give you insight into your health, predict your menstrual cycle safe days and fertile days, and record cycle length and symptoms so you can see tendencies over time.

Plan or prevent pregnancy

Each cycle has a fertility window of 5–6 days when a woman can get pregnant. It takes only 12–24 hours for a mature egg (usually only one) to burst from its follicle in the ovary and travel down the fallopian tube to the uterus. If fertilised in that time, the egg will implant in the uterine lining, and pregnancy will begin. If not, the egg will disintegrate and flow away with the menstrual blood. However, sperm can live up to 5 days in the reproductive tract. Unprotected sex five days before and up to 24 hours after ovulation can lead to pregnancy. With regular use, our app can provide a fertility forecast for the days you are most likely to get pregnant. While not a replacement for contraception, this level of fertility awareness can complement your other practices.

It helps your doctor

Whenever you visit your gynaecologist, the first questions tend to be: When did your last period start? How long and heavy was it? Do you have any associated recurring symptoms? Being able to share accurate information with your doctor brings them into the picture faster so you can make the best possible decisions about your health.

Track your cycle with the WomanLog period calculator

A period calculator is a great way to track your cycle, watch your health, and boost your awareness of the changes that happen in your body. Start period planning, fertile day forecasts, and in-depth statistics for your cycle with the WomanLog period tracker.

The mobile app version allows you to track your cycle, fertile days, weight, moods, and related health symptoms on the go. Try the WomanLog free period calculator now!

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