Are you constantly counting on your fingers to figure out where you are in your cycle? Are you wondering if your next period will fall right on your vacation? Or are you trying to pinpoint your fertile window without losing your mind? This tool is for you. A simple, comprehensive, and visual calculator that tells you exactly where you are, what's happening in your body, and what's coming up in the next few days.
⚡ What this tool does for you
Your Personalized Cycle Calculator
Fill in these three basic pieces of information and the tool will calculate everything else. If you don't know your exact cycle length, 28 days is the average, but it can range from 21 to 35 days (and that's normal).
Average: 28 days · Normal: 21-35 days
⚠️ Important Disclaimer : This calculator provides estimates based on a regular cycle. Every body is different, and many factors (stress, diet, sleep, illness) can delay ovulation and periods. This tool is not a substitute for medical supervision, especially if you are using natural birth control or trying to conceive. If your cycle is very irregular, consult a healthcare professional.
How to Use This Tool Effectively
To get accurate results, you need three basic pieces of information. If you don't know them yet, don't panic—here's how to find them.
1. The first day of your last period
This is the day your period actually started (not the light spotting from the day before). This is called Day 1 (D1) of your cycle. All calculations start from this date. If you can't remember the exact date, try to find a calendar or a photo from this period.
💡 Tip : Get into the habit of writing this date down every month in your phone or notebook. It makes everything easier.
2. The usual length of your cycle
This is the number of days between the first day of your period and the first day of your next period. The average is 28 days, but a normal cycle can range from 21 to 35 days. If your cycles are irregular (plus or minus 7 days of variation), take an average of the last 3 cycles.
📊 Example : Last period on January 1st, new period on January 29th → 28-day cycle
3. The length of your period
How many days you bleed on average (from the first to the last day, even if the flow decreases). The average is 5 days, but between 3 and 7 days is normal. This information allows the calculator to accurately display your menstrual phase in the timeline.
What's the Real Use of Calculating Your Cycle?
Beyond knowing when to buy tampons, knowing your cycle gives you a level of control and understanding of your body that few women have. Here are the concrete benefits.
🎯 Optimize or avoid pregnancy
If you're trying to conceive, you know exactly which days to have intercourse. If you want to avoid pregnancy naturally (symptothermal method), you identify your fertile window. Be careful, this method requires rigorous training and is not suitable for everyone.
📅 Anticipate the unexpected
Vacations, job interviews, weddings, intense workouts... You can plan ahead knowing exactly when your period will arrive. No more unpleasant surprises in a swimsuit or white pants.
(I.e. Understanding your mood swings
If you're feeling irritable, anxious, or tired, a look at your cycle can explain why. Hormones influence your mood, energy, libido, and even digestion. It's not "in your head," it's biological.
🩺 Detect anomalies
A very short (less than 21 days), very long (more than 35 days), or very irregular cycle may indicate a hormonal imbalance, chronic stress, PCOS, or a thyroid problem. The tracker allows you to see these patterns and speak to a doctor if necessary.
The 4 Phases of Your Cycle Explained
Your menstrual cycle is divided into four distinct phases, each with its own dominant hormones and effects on your body and mood. Understanding these phases allows you to adapt your daily life (exercise, work, social life) to your natural energy.
🩸 Menstrual Phase (approximately D1-5)
The first day of your period marks the beginning of a new cycle. Your uterus sheds the thickened lining (endometrium) in the form of bleeding. Estrogen and progesterone levels are at their lowest, which can leave you feeling tired and withdrawn.
What's happening in your body
- Bleeding (light to heavy flow depending on the day)
- Possible uterine cramps (due to prostaglandins)
- Fatigue, need rest
- Food cravings, sometimes disturbed digestion
🌱 Follicular Phase (approximately D6-13)
After your period, your body prepares for another ovulation. Several follicles (small sacs each containing an egg) begin to mature in your ovaries. A dominant follicle will eventually prevail and prepare to release its egg. Estrogen levels gradually rise, improving your mood, energy, and confidence.
What's happening in your body
- Boost of energy and motivation
- Brighter skin, more beautiful hair
- Positive mood, increased sociability
- Cervical mucus becomes creamier
- It's the perfect time to start new projects
🥚 Ovulatory Phase (approximately D13-15) - PEAK FERTILITY
Ovulation generally occurs 14 days before your next period (in the middle of a 28-day cycle, but delayed if your cycle is shorter or longer). The dominant follicle releases its egg, which is captured by the fallopian tube. The egg survives for a maximum of 12 to 24 hours. This is THE time of maximum fertility.
What's happening in your body
- Maximum energy, confidence in yourself
- Increased libido (it's biological)
- Clear, egg-white cervical mucus
- Slight rise in basal temperature after ovulation
- Some women feel a little pain on one side (mittelschmerz)
- Fertile window: 5 days before ovulation + day of ovulation
🍂 Luteal Phase (approximately D16-28)
After ovulation, the empty follicle transforms into a corpus luteum, which produces massive amounts of progesterone. This hormone prepares the uterus to receive a potential embryo (a very thick and vascularized endometrium). If the egg is not fertilized, the corpus luteum degenerates 12-14 days after ovulation, progesterone levels drop, and menstruation arrives.
What's happening in your body
- Energy that gradually decreases
- Possible PMS at the end of the phase (irritability, fatigue, bloating, acne)
- Slightly higher basal temperature
- Food cravings (especially sweet/fatty)
- Tender or swollen breasts
- Need rest, want to cocoon
🌙 Understanding Your Luteal Phase (Symptoms, Duration & Fertility) →
Why the Fertile Window Lasts 6 Days (Not Just D-Day)
If the egg only survives for 12-24 hours, why do we talk about a 6-day fertile window? This is where biology gets fascinating.
🏊 Sperm are marathon runners
Unlike the egg, which dies quickly, sperm can survive for up to 5 days in your reproductive tract, provided there is fertile cervical mucus to nourish and protect them. They "stand by" in the crypts of the cervix and fallopian tubes.
So the fertile window is
- 5 days before ovulation : the sperm arrive and patiently wait for the egg
- The day of ovulation : last chance, sperm must be there within 24 hours
Concretely, if you have intercourse 3 days before ovulation, the sperm can remain alive and fertilize the egg on the day. This is why natural contraception requires abstention or the use of protection during this entire 6-day window.
Protect yourself throughout your cycle
Whether you're ovulating or menstruating, our period panties offer comfort and protection. They're also perfect for vaginal discharge during your fertile period.
Situations Where the Calculator Is Less Reliable
This tool works on the principle that your cycles are relatively regular. But several situations can make predictions less accurate.
Very irregular cycles (variation of more than 7 days)
If your cycles vary by 25 to 38 days from month to month, it's impossible to accurately predict your ovulation. Causes could include PCOS, thyroid imbalance, chronic stress, or perimenopause. In this case, combine the tool with cervical mucus monitoring and/or ovulation tests.
Recent discontinuation of hormonal contraception
After stopping the pill, implant, or hormonal IUD, it can take several months for your body to return to regular, ovulatory cycles. The first cycles are often chaotic. Be patient; they will stabilize (usually within 3-6 months).
Postpartum and breastfeeding
After giving birth, the return of menstruation varies greatly (from a few weeks to more than a year if you are exclusively breastfeeding). Breastfeeding can block ovulation in unpredictable ways. The calculator will only be reliable once you have had at least 2-3 regular cycles.
Severe stress or life change
Major stress (bereavement, moving, exams, breakups), travel with jet lag, rapid weight loss or gain, or illness can delay your ovulation or even block it completely that month. The cycle can be extended by several days or weeks.
Very young cycle or premenopause
The first few years after menarche (puberty) and the years before menopause (perimenopause, usually after age 45) are characterized by irregular cycles. This is normal, but it makes predictions difficult.
Track Your Symptoms: Why It's Useful
The tool's "symptom tracker" section isn't just a gimmick. Regularly recording your mood, energy, and physical symptoms allows you to detect patterns you hadn't noticed.
What you can discover by tracking
- Your PMS has a logic : if you systematically note "irritable + tired + bloated" on days 24-26, it's not a coincidence, it's your PMS. You can anticipate and adapt your schedule (avoid stressful meetings on these days if possible).
- Some symptoms are related to ovulation : If you still have a headache on days 13-15, it may be the sudden drop in estrogen just after ovulation. Knowing this allows you to have painkillers on hand.
- Abnormal patterns emerge : if you notice "intense cramps + heavy bleeding" every month, it's worth talking to a gynecologist (possible endometriosis, fibroids, etc.).
- You understand your libido fluctuations : peak of desire at ovulation (normal, it's biology), drop in the luteal phase (also normal). This avoids feeling guilty.
The data you enter into the tracker is saved locally on your device (in your browser's storage). It is never sent to an external server. It's private, it's for you.
Optimize Your Tracking Accuracy
The calculator gives you estimates, but you can improve their accuracy by combining several observation methods. The more you know your body, the more accurate the predictions will be.
🌡️ Combines with basal temperature
Basal body temperature (when you wake up, before getting up) increases by 0,3 to 0,5°C just after ovulation and remains high until your period. By measuring it every morning, you can retrospectively confirm that ovulation has occurred.
How to do
- Take your temperature every morning at the same time (preferably before 8 a.m.)
- Use a thermometer accurate to within 0,1°C (special basal temperature)
- Mark it on a chart to see the upward pattern
- If your temperature remains high beyond 18 days, you are probably pregnant.
💧 Observe your cervical mucus
Cervical mucus is the most reliable indicator of your impending ovulation. It changes texture throughout your cycle, going from sticky and thick to clear and stretchy (egg white-like) just before ovulation.
What you are looking for
- Right after your period : dry or sticky (infertile)
- Approaching ovulation : creamy, white (transition)
- ovulation : transparent, elastic, stretches between your fingers (fertile ✨)
- After ovulation : becomes thick again or disappears (infertile)
🧪 Use ovulation tests (optional)
Ovulation tests detect the LH (luteinizing hormone) surge that occurs 24-36 hours before ovulation. They are especially useful if you are trying to conceive or if your cycles are irregular.
💡 Tip: Combines calculator + mucus + ovulation test for maximum accuracy. Start testing 3-4 days before the ovulation date predicted by the calculator.
Irregular Cycles: Adapting the Tool to Your Reality
If your cycles vary by more than 7 days from month to month, the calculator will be less accurate. Here's how to use it anyway and what to look out for.
Calculates a moving average
Note the duration of your last 3-6 cycles, then take an average. For example:
Cycle 1: 26 days
Cycle 2: 32 days
Cycle 3: 29 days
Cycle 4: 31 days
Average: (26+32+29+31) ÷ 4 = 29,5 days → Between 29-30 days in the calculator
This average will give you a central estimate, but allow for a margin of error of ±5 days.
Identify the causes of the irregularity
Uncontrolled cycles can have several causes. Some are temporary, others require medical attention.
Stress can delay or block ovulation. Solutions: rest, yoga, and adjusting your lifestyle.
Frequent hormonal imbalance (5-10% of women). Symptoms: long cycles, acne, hair growth. Consult a gynecologist.
Hypo or hyperthyroidism disrupts the cycle. Simple blood test to check (TSH, T3, T4).
Rapid weight loss or gain (>10kg in a few months) can disrupt the cycle.
Too much exercise with few calories can block ovulation (hypothalamic amenorrhea).
Use the Calculator to Design
If you're trying to get pregnant, the calculator tells you exactly when to focus your efforts. But beware of the misconceptions circulating on forums.
The optimal timing of reports
Contrary to popular belief, you should not wait until the exact day of ovulation. Sperm need time to ascend and become capacitated (prepare to fertilize).
Recommended frequency
- Ideal : intercourse every 2-3 days throughout the fertile window (6 days)
- The 2 best days : D-2 and D-1 before ovulation (30-35% chance of conception)
- D-day : the day of ovulation itself (20% chance)
- After ovulation : too late, the egg only survives 12-24 hours
💡 Myth to forget: "You have to wait several days between intercourse to build up sperm." False. Sperm quality is better with regular ejaculations (every 2-3 days) than with ejaculations spaced a week apart.
Don't become obsessed with timing
Too much pressure and calculations can make intercourse mechanical and stressful, which is counterproductive. Stress can even delay ovulation.
Tips for de-stressing
- Having regular intercourse throughout the year (2-3x/week) automatically covers the fertile window
- Maintains fun and spontaneity even during the fertile period
- Avoid testing too early (at least wait until your period is late so you don't worry about false negatives)
- If nothing after 12 months of regular testing (or 6 months after age 35), consult a fertility specialist
Comparison: Calculator VS Tracking Apps
You might be wondering why you should use this tool instead of a cycle tracking mobile app. Here are the concrete differences.
💡 Our advice: Use this tool for a quick, up-to-date view of your cycle. If you want detailed tracking over several years with history, graphs, and reminders, complete it with a reputable app (Clue, Flo, Natural Cycles for symptothermal method). Avoid apps that resell your data (read their privacy policies).
Frequently Asked Questions
10 Menstrual Cycle Myths You Need to Stop Believing
Forums and old family beliefs carry many misconceptions about the cycle. Let's sort out the truth from the lies once and for all.
Myth 1: “All cycles last 28 days”
False. Only 15% of women have a cycle of exactly 28 days. Normal is 21 to 35 days. Your 32-day cycle isn't "abnormal," it's just your cycle.
Myth 2: “Ovulation always occurs on day 14”
False. Ovulation occurs about 14 days BEFORE your next period, not 14 days after your period starts. If your cycle is 35 days long, you ovulate around day 21, not day 14. That's why the calculator adjusts everything based on your cycle length.
Myth 3: “You can’t get pregnant during your period.”
Almost false. If you have a very short cycle (21 days) and a long period (7 days), you can ovulate on days 7-8. Intercourse on day 5 + sperm that survive 5 days = possible fertilization. Rare, but not impossible. Never rely on your period as contraception.
Myth 4: “Irregular cycles are always serious.”
False. A variation of 2-7 days from one cycle to the next is common and normal. However, cycles that vary by more than 10 days or a complete absence of periods for 3+ months warrant a consultation.
Myth 5: “You have to space out intercourse to build up sperm.”
False. Sperm quality is better with regular ejaculations (every 2-3 days) than with ejaculations spaced a week apart. Waiting mainly "accumulates" old, less motile sperm.
Myth 6: “Painful periods are normal, you have to grit your teeth.”
False. Mild cramps are common, but pain that prevents you from living a normal life (work, school, going out) is NOT normal. It could be endometriosis, adenomyosis, or fibroids. Seek help; solutions exist.
Myth 7: "We ovulate on both sides alternately"
False. There is no strict right-left alternation. It's random depending on which follicle matures first that month. You can ovulate on the same side for several months in a row.
Myth 8: “PMS is just mental, it’s in the head.”
False. PMS (premenstrual syndrome) is caused by real hormonal fluctuations (drops in progesterone and estrogen). The symptoms are real: irritability, fatigue, bloating, migraines. It's not "being crazy," it's biology.
Myth 9: "After stopping the pill, you get pregnant immediately."
Not necessarily. It can take 1-6 months (sometimes longer) for your body to return to regular ovulatory cycles after stopping hormonal contraception. This is normal, so be patient. If you don't see any improvement after 12 months of trying, consult a doctor.
Myth 10: “Vegetarian discharge is dirty, you have to get rid of it.”
False. Cervical mucus (white discharge) is natural, healthy, and necessary. It protects your vagina from infections and aids fertility. NEVER douche to "clean" the insides; it unbalances your flora.
Lifestyle: What Affects Your Cycle (And How to Improve It)
Your cycle isn't just about your hormones. Your lifestyle plays a major role in its regularity, the quality of your ovulation, and the intensity of your symptoms.
💧 hydration
Drinking 1,5-2L of water per day improves the quality of your cervical mucus (it is 90% water). Chronic dehydration can make the mucus thicker and less fertile.
Concrete action: Always keep a water bottle with you
???? Balanced diet
Restrictive diets, lack of healthy fats, or iron/magnesium/B6 deficiencies can block ovulation or worsen PMS. Focus on green vegetables, nuts, and oily fish.
Concrete action: Add a handful of nuts/almonds daily
😴 Quality sleep
Chronic sleep deprivation (less than 7 hours/night) disrupts melatonin production, which disrupts your reproductive hormones. Irregular sleep patterns can delay your ovulation.
Concrete action: Go to bed at regular times, even on weekends.
🏃♀️ Moderate sport
Regular physical activity (30 minutes 3-5 times a week) improves circulation, reduces PMS, and regulates hormones. But too much intense exercise (marathon, daily CrossFit) can block ovulation.
Concrete action: Walk 30 min/day or yoga 3x/week
🧘♀️ Stress management
Chronic stress increases cortisol, which can block ovulation (the hypothalamus-pituitary-ovarian axis is disrupted). The cycle can lengthen by several weeks or stop completely.
Concrete action: 10 minutes of deep breathing/meditation per day
(I.e. Tobacco and alcohol
Smoking reduces ovarian reserve and brings menopause forward by several years. Regular alcohol consumption (more than 7 drinks/week) disrupts hormonal balance and can lengthen the cycle.
Concrete action: Limit to 1-2 drinks/week max, quit smoking
The winning combo for an optimal cycle
You don't need to be perfect in every way. Choose 2-3 realistic areas for improvement and stick to them for 3 months. The effects on your cycle will gradually become noticeable (better regularity, fewer PMS, clearer ovulation).
🎯 3-month action plan: Increase your hydration + take magnesium (300mg/day) + sleep 7-8 hours/night. Record changes in the tool's symptom tracker to see how they're progressing.
Print or Share Your Results
Want to keep track of your calculations or show them to your doctor? Here's how to save your results.
📸 Take a screenshot
The easiest and fastest method.
🖨️ Print the page
Use your browser's print function (Ctrl+P or Cmd+P). You can also choose "Save as PDF" as your printer to create a file that you can email.
📱 Add to favorites
Bookmark this page to easily find it each month. On mobile, you can also add it to your home screen for quick access ("Share" icon then "On Home Screen").
Sources & Scientific References
The calculations in this tool are based on validated scientific data regarding average cycle length, ovulation timing and gamete survival.
Studies on ovulation and the fertile window
- Wilcox AJ, Dunson DB, Weinberg CR, et al. (1995). Timing of sexual intercourse in relation to ovulation: effects on the probability of conception, survival of the pregnancy, and sex of the baby. New England Journal of Medicine. DOI: 10.1056/NEJM199512073332301
- Wilcox AJ, Baird DD, Weinberg CR. (1999). Time of implantation of the conceptus and loss of pregnancy. New England Journal of Medicine. DOI: 10.1056/NEJM199906103402304
- Colombo B, Masarotto G. (2000). Daily fecundability: first results from a new data base. Demographic Research. DOI: 10.4054/DemRes.2000.3.5
Length and variability of menstrual cycles
- Münster K, Schmidt L, Helm P. (1992). Length and variation in the menstrual cycle - a cross-sectional study from a Danish county. British Journal of Obstetrics and Gynecology. DOI: 10.1111/j.1471-0528.1992.tb13635.x
- Bull JR, Rowland SP, Scherwitzl EB, et al. (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. NPJ Digital Medicine. DOI: 10.1038/s41746-019-0152-7
Cycle tracking methods and effectiveness
- Ecochard R, Duterque O, Leiva R, et al. (2015). Self-identification of the clinical fertile window and the ovulation period. Fertility and Sterility. DOI: 10.1016/j.fertnstert.2014.10.023
- Fehring RJ, Schneider M, Raviele K. (2006). Variability in the phases of the menstrual cycle. Journal of Obstetric, Gynecologic & Neonatal Nursing. DOI: 10.1111/j.1552-6909.2006.00051.x
Note: DOI links provide direct access to the original scientific publications. The calculations performed by this tool are statistical estimates based on this data, but cannot replace personalized medical monitoring.
Medical Warning: This tool is intended for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. For any questions regarding your reproductive health, cycle, or fertility, consult a gynecologist, midwife, or medical specialist.
