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How to Calculate Next Period Date

Cycle Syncing | By: Katie Lister

February 18, 2024

How do I calculate my next period? How many days are there between periods? Why does my period date keep changing? If you find yourself asking these questions and more on how to calculate next period date, you have come to the right place.

Hi, my name is Katie Lister, the founder of Growth Gals (GG) and a Registered Nurse. I lead personal development groups and communities and coach women to step into the best versions of themselves.

GG provides women with a safe space to come together to learn and get support from other like-minded women. At GG, we discuss various aspects of women’s reproductive health, such as predicting your next period.  This article will provide the information you need about how to calculate the next period date and more.

Table of Contents

Katie Lister

Katie Lister

Written by Katie Lister, RN, BScN. An experienced Registered Nurse, Group Facilitator, Life Coach, and Community Leader. Read Katie's Full Author Bio

Understanding the Menstrual Cycle

Your menstrual cycle begins when you menstruate or get your period. Female hormones in your body control the process as they prepare your body for pregnancy. Your body goes through different changes in each of the four menstrual cycle distinct phases, which are:


The first day of your period marks the beginning of your new menstrual cycle. Periods are a natural process where the uterus sheds its lining and releases blood and tissue from the vagina. They occur when you do not conceive in the previous month and happen on average every 28 to 30 days, lasting for 3 to 7 days.

Symptoms of menstruation include:

  • Mood changes
  • Cramps
  • Insomnia
  • Breast tenderness
  • Headaches
  • Bloating
  • Food cravings

Follicular phase (days 1 to 14)

The menstrual cycle’s follicular phase lasts from approximately day 1 to day 14. The Follicle-stimulating hormone (FSH) causes several follicles to rise on the surface of the ovary, each containing an egg. Eventually, one follicle becomes dominant, and a single mature egg develops within it.

High estrogen levels stimulate the production of the gonadotropin-releasing hormone (GnRH), which promotes the secretion of the luteinizing hormone (LH). Around day 12, the follicle releases the egg, and testosterone briefly rises, increasing your sex drive.

Ovulatory phase (Day 14)

Ovulation is the shortest phase that lasts about 24 hours. As a result of the FSH and LH surge, the follicle releases the mature egg around day 14. The egg goes into the fallopian tube, where fertilization may occur if it meets with sperm. If not fertilized, the egg disintegrates after approximately 24 hours. After the follicle releases the mature egg, it seals over and becomes the corpus luteum.

Luteal Phase (Days 14 to 28)

After the follicle releases the egg, the hormone levels (FSH and LH) decrease, and the corpus luteum starts to produce progesterone, which thickens the lining of the uterus in readiness for pregnancy. If fertilization does not happen, the corpus luteum disintegrates and becomes reabsorbed into the body. The disintegration of the corpus luteum causes your progesterone levels to decrease, signaling the shedding of the endometrial or uterus lining.

Feeling tired after ovulation? here is how to ease the symptom. 

Regular vs. Irregular Cycles

The average menstrual cycle is a 28-day cycle; although a normal cycle can range from twenty-one to thirty-five days. If your period follows a pattern, it’s a regular menstrual cycle. However, when the period is inconsistent, it’s an irregular period and may occur due to different reasons, such as:

  • Hormonal imbalances: Hormonal imbalances can cause irregular periods. For instance, if your thyroid hormones rise or fall drastically, or if you have excess androgen, a hormone that causes hair growth on the chin, face, abdomen, or chest, and also leads to weight gain.
  • Health conditions: Health conditions like endometriosis, polycystic ovarian syndrome (PCOS), endometriosis, or eating disorders can cause irregular periods
  • Stress can cause you to get early periods or a delay. If you are constantly stressed, your period may become erratic.
  • Medication: If you are under medication like blood thinners (anticoagulants) or steroids
  • Endurance exercise such as gymnastics or long-distance running
  • Starting or stopping contraception methods such as birth control pills

Some women have irregular cycles that range from menstruating every several months or twice a month. If your periods are consistently irregular, you should seek medical advice, as it could mean an underlying condition.

How to Calculate Next Period Date and Ovulation Time without an App

Tracking your period and ovulation is especially important if you are trying to conceive. The average period length and menstrual cycle vary from woman to woman.

To calculate your menstrual cycle length, count the days between the start of your period and the start of your next period. Add the total number of days and divide by the number of cycles recorded.  For example, for 6 cycles, divide the total by 6 for the average cycle length.

Your body is the most accurate predictor of your incoming period as it gives you numerous signs. Approximately, 80 and 90% of women get period symptoms also known as PMS (premenstrual syndrome). To foretell your next period date, you must track your period for a while to get a pattern.

Most women ovulate approximately halfway into their menstrual cycle, which, on average, is about 28 or 29 days. However, some women may have shorter or longer menstrual cycles. You can estimate your ovulation date by subtracting 14 days from the expected date of your next period.

For example, if your cycle runs for 28 days, your day of ovulation will fall on day 14. Your ovulation may depend on the regularity and length of your menstrual cycle. Your fertile window falls on the five days before ovulation, the ovulation day, and the next day.

You can also tell when you are ovulating by:

  • Basal body temperature: This involves tracking your temperature at rest (97 or 97.5) Ovulation causes a slight increase in temperature, (97.6 or 98.6) and you are most fertile two to three days before it rises. Monitoring your basal body temperature each day can help you predict ovulation and determine the best time to conceive.
  • By your vaginal discharge: It is clear and stretchy and looks like egg white when you are ovulating.
  • By using an ovulation predictor kit (OPK) to gauge when you’re ovulating. These kits detect a spike in luteinizing hormone (LH), which your body starts releasing about 36 hours before you ovulate.
  • By using an online ovulation calculator

How To Calculate Next Period Using Period Calculators/Apps

Period tracking apps allow women to monitor their menstrual cycles, predict period dates, and provide forecasts on their ovulation and fertile days. Cycle-tracking apps store and analyze various data related to your menstrual cycle. This data includes information like your past periods, heart rate, sleep patterns, cervical secretions, and basal body temperature.

Enter all this data into the app, which will use it to make predictions about when to expect your period and when you are most likely to ovulate. A period calculator becomes effective depending on how diligent you are in feeding it data about your period cycle. To know the best pre-period predictor app, consider:

  • Asking your OB-GYN to recommend one
  • Doing your due diligence to find out who built the app and their professional credentials. Go to their website FAQs (frequently asked questions) and read the questions people ask.
  • Check how much data the app collects. The more data the app collects, the better it can predict. An app collecting only dates of your last period is not the same as one collecting your cervical mucus amount and basal temperatures.
  • Ease of use:  Ensure the app is easy to use

Some of the best period tracking apps in the market include:

  • Flo Period and Pregnancy Tracker
  • Spot on
  • Clue Period Tracker & Calendar

Can You Calculate the Period Date If Your Cycles Are Irregular?

An irregular menstrual cycle falls outside the normal range of 21 to 35 days and could come earlier, later or not come at all. To calculate your cycle length, record your periods’ duration and heaviness by using a paper or digital (phone) calendar. Tracking PMS symptoms can also help you know when your menstrual period is on its way.

Detecting patterns in your menstrual cycles is the first step to determine if you have irregular periods. You can track ovulation by observing changes in cervical mucus and basal body temperature. Use ovulation predictor kits or observe changes to know when you’re ovulating and approximate future periods.

Luteal phase foods and follicular phase foods you should be eating to regulate your cycle. 

How to Calculate Next Period Date: How Growth Gals Can Help

At Growth Gals, we aim to inspire women to reach their full potential. We also strive to create positive change by offering resources that help to expand their knowledge base. Growth Gals helps women overcome obstacles and learn more about topics on women’s health, such as how to calculate your next period date.

At GG, we help to propel you toward your period-tracking efforts and help you navigate topics like period and ovulation tracking.

Subscribe to the Growth Gals newsletter to gain access to even more helpful guides and resources. Get updates on our coaching, support group, retreats, and more. Learn more about how we can support you, help you live your best life, and evolve into the best version of yourself!

How to Calculate Next Period Date: Conclusion

You can track your next period date and your menstrual cycle, either manually or using a cycle calculator. A normal menstrual cycle is approx. 28 or 29 days from person to person. You can track your menstrual cycle, your period, and your ovulation, either manually or via apps that you download on your smartphone. If your period is highly irregular, talk to a healthcare provider to rule out underlying conditions.

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