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Period calculator: Predict your next menstrual cycle
Track your cycle
Enter your details below to get an instant estimate of your cycle.
Select the first day you experienced actual bleeding, not just light spotting.
The number of days from the start of one period to the next. The average is 28 days, but adult cycles can commonly vary between 21 to 35 days.
How many days your bleeding usually lasts. The average is 4 to 6 days.
Please enter a valid last period date.
Your Cycle Estimates
Based on your history, here are your upcoming predicted dates.
How does the period calculator work?
A period cycle calculator works by taking the first day of your last menstrual period (LMP) and adding your average cycle length to estimate when your next period will begin. For example, if your cycle is 28 days long, the calculator predicts your next period will start approximately 28 days after your last one began.
It also estimates ovulation, which usually occurs 14 days before your next period, to highlight your estimated fertile window. These are estimated based on averages, not exact predictions, since cycles can vary from month to month. It also works best for regular cycles and can be inaccurate if your cycle varies, ir you’ve recently started or stopped the pill, or if you’ve recently given birth or are breastfeeding.
The 4 phases of your menstrual cycle
| Phase | Roughly when | What’s happening |
|---|---|---|
| Menstruation | Days 1-5 | The uterine lining sheds. Oestrogen and progesterone drop, causing fatigue, cramping, and low energy. |
| Follicular phase | Days 1-13 | Overlaps with menstruation. The pituitary gland releases follicle-stimulating hormone (FSH), and rising oestrogen tends to boost energy, mood and focus. |
| Ovulation | Around day 14 | A surge in luteinising hormone (LH) triggers the release of a mature egg. This is your most fertile time of the cycle and includes the 5 days before ovulation and the day of ovulation. |
| Luteal phase | Days 15-28 | Progesterone rises to prepare the uterus for a possible pregnancy. If the egg isn’t fertilised, hormone levels fall, triggering PMS symptoms in some women such as bloating, mood changes and breast tenderness. |
What is a normal vs an irregular period?
While 28 days is usually quoted as the clinical average, a healthy menstrual cycle can range anywhere from 21 to 35 days in adults, and up to 45 days in teenagers, especially in the first few years after periods start. There’s a broad range of what’s considered normal, and your cycle may simply differ from someone else’s.
A period may be considered irregular if:
- Your cycle length varies significantly from month to month
- Bleeding lasts longer than 7 days
- Your flow is exceptionally heavy, such as soaking through a pad or tampon every 1 to 2 hours.
Irregular periods are quite common and can have several causes, including polycystic ovary syndrome (PCOS), endometriosis, thyroid issues, or extreme stress. If your menstrual cycle consistently falls outside these ranges, it’s worth discussing with a doctor rather than waiting to see if it improves on its own.
Why is my period late? (top 5 reasons)
A late period can be stressful, but there can be several reasons your cycle might be running behind schedule:
- Stress: Physical and emotional stress can disrupt the hormones that regulate your cycle.
- Significant weight change: Rapid weight loss or gain can affect ovulation and cause your menstrual cycle to become irregular.
- Intense exercise: A sudden increase in the intensity or volume of exercise may delay ovulation.
- Hormonal birth control changes: Starting, stopping, or switching contraception may temporarily affect your menstrual cycle.
- Underlying health conditions: Conditions such as polycystic ovary syndrome (PCOS) or thyroid disorders can interfere with ovulation and affect the cycle regularity.
If your period is overdue and there’s a chance you could be pregnant, take a pregnancy test. If your period is consistently late or absent, it’s a good idea to speak with a doctor to explore the possible causes. Seek urgent medical care if you have severe one-sided pelvic pain, pain in your shoulder tip area, feeling faint or dizzy, or have heavy bleeding, as these can be warning signs of an ectopic pregnancy.
Menstrual cycle FAQs
1. How accurate is my period predictor?
2. Can stress delay your period?
3. What if I don’t know my average cycle length?
4. Can a doctor help with irregular periods?
5. Is it normal to miss a period if I’m not pregnant?
6. Can I get a doctor’s note for period pain?
7. How long should my period last?
8. What are some signs my period is coming?
9. Why is it important to track my menstrual cycle?
10. When do periods stop?
11. Why is my period so irregular?
Speak to an Australian-registered doctor online
Planning for a baby? Connect with an Australian-registered doctor from the comfort of your home. A Hola Health online doctor can help you with:
- Referrals to gynaecologists and fertility specialists
- PCOS care and management
- Help with general reproductive health concerns
Available 24 hours, on weekends, on public holidays, and with no waiting room. Visit Hola Health to book your consultation today. Call 000 for emergency.
