Ovulation Calculator
Calculate your ovulation day and fertile window based on your last menstrual period and cycle length. Identify up to 6 fertile days each month for conception planning.
Menstrual Cycle Tracker Calculator
Track your menstrual cycle phases — follicular, ovulatory, and luteal. Predict next period date, PMS window, and cycle regularity from your average cycle length.
⚠️ Medical Disclaimer: This calculator provides estimates for educational purposes. Actual cycle timing varies. It is not a reliable method of contraception. Consult your healthcare provider for any concerns about your menstrual health.
days
days
🌹
Today is Cycle Day
1
Menstruation
28 days until next period
1
PeriodFollicularOvLutealPMS
Current Phase⧉
Menstruation
Day 1 of 28
Next Period⧉
May 27, 2026
28 days away
Follicular Phase⧉
14 days
Days 1 to ovulation
Luteal Phase⧉
14 days
Ovulation to period
Cycle Phases This Month
| Phase | Days | What Happens |
|---|---|---|
| 🌹 Menstruation ◀ | Days 1–5 | Uterine lining sheds; bleeding occurs |
| 🌱 Follicular Phase | Days 6–12 | Estrogen rises; follicles develop; energy increases |
| 🌸 Ovulation Window | Days 12–15 | LH surge; egg released; peak fertility |
| 🌙 Luteal Phase | Days 16–21 | Progesterone rises; uterine lining thickens |
| ⚡ PMS Window | Days 22–28 | Progesterone drops; PMS symptoms may appear |
Next 6 Periods
| # | Period | Ovulation | PMS Starts |
|---|---|---|---|
| 1 | May 27 – May 31 | Jun 9 | Jun 16 |
| 2 | Jun 24 – Jun 28 | Jul 7 | Jul 14 |
| 3 | Jul 22 – Jul 26 | Aug 4 | Aug 11 |
| 4 | Aug 19 – Aug 23 | Sep 1 | Sep 8 |
| 5 | Sep 16 – Sep 20 | Sep 29 | Oct 6 |
| 6 | Oct 14 – Oct 18 | Oct 27 | Nov 3 |
Planning notes, formulas, and examples
About the Menstrual Cycle Tracker Calculator
The Menstrual Cycle Tracker Calculator helps you understand and predict your cycle phases. By entering your last menstrual period (LMP) date and average cycle length, you can see when each phase of your cycle occurs: menstruation, follicular phase, ovulation window, and luteal phase.
Understanding your cycle phases can help you anticipate PMS symptoms, plan around your likely fertile window, and notice patterns that may be worth discussing with a clinician. The average menstrual cycle is 28 days, but normal cycles range from 21 to 35 days in adults.
This calculator also projects your next 6 periods and PMS windows so you can plan ahead for travel, events, and activities.
When This Page Helps
Cycle tracking helps you anticipate recurring patterns such as menstruation, PMS, and the broader fertile window. It can also make it easier to notice when cycle timing changes enough to justify a medical discussion.
How to Use the Inputs
- Enter the first day of your last menstrual period.
- Enter your average cycle length (21–45 days).
- Enter your typical period duration (2–8 days).
- View your current cycle day and phase.
- See the next period prediction and PMS window.
- Review the 6-cycle projection table.
Formula used
Cycle Day = (Today − LMP) mod Cycle Length + 1
Phases:
• Menstruation: Days 1–(period length)
• Follicular: Days 1–(Cycle Length − 14)
• Ovulation Window: (Cycle Length − 16) to (Cycle Length − 12)
• Luteal Phase: (Cycle Length − 13) to Cycle Length
• PMS Window: ~7 days before next period
Next Period = LMP + Cycle Length
Luteal Phase = Cycle Length − Ovulation Day
Ovulation Day ≈ Cycle Length − 14Example Calculation
Result: Current: Day 12 (Follicular) | Next Period: March 1 | PMS: Feb 22–28
Assuming today is February 12: Cycle day 12, in the late follicular phase. Ovulation is expected around day 14 (February 15). The luteal phase starts after ovulation and lasts ~14 days. Next period expected March 1. PMS symptoms may begin around February 22 (7 days before the next period).
Tips & Best Practices
- Track your cycle for at least 3–6 months to establish your personal pattern before relying on predictions.
- Normal cycle length variation of ±2–3 days cycle-to-cycle is common and not a concern.
- PMS symptoms (bloating, mood changes, breast tenderness) typically start 7–10 days before your period.
- Cycles shorter than 21 days or longer than 35 days should be discussed with your healthcare provider.
- Stress, significant weight changes, excessive exercise, and illness can all shift your cycle temporarily.
- Consider using a physical or app-based calendar to log symptoms alongside dates for a complete picture.
Understanding Cycle Phases
The follicular phase begins on the first day of menstruation and continues until ovulation. During this phase, the pituitary gland stimulates FSH production, which drives follicular development in the ovaries. Estrogen rises progressively, thickening the uterine lining and triggering the LH surge that causes ovulation.
The luteal phase begins after ovulation and lasts until the next period. The ruptured follicle becomes the corpus luteum, which produces progesterone to maintain the uterine lining for potential embryo implantation. If pregnancy does not occur, the corpus luteum degenerates, progesterone drops, and menstruation begins.
When to See a Doctor
Consult a healthcare provider if you experience cycles shorter than 21 days or longer than 35 days consistently, missed periods (while not pregnant), extremely heavy bleeding (soaking a pad/tampon hourly), severe pain that interferes with daily activities, or bleeding between periods. These symptoms can indicate treatable conditions.
Sources & Methodology
Last updated:
Methodology
This worksheet estimates phase timing from the first day of the last menstrual period and the average cycle length. It uses simple calendar-based phase approximations rather than hormone measurements, ultrasound, or fertility testing.
The output is intended as a planning aid for cycle tracking, not a diagnostic fertility or gynecologic assessment.
Sources
- Menstrual Cycle and Ovulation (NICHD) — Cycle phase timing and general cycle-length context.
- Menstruation in girls and adolescents: using the menstrual cycle as a vital sign (AAP / ACOG) — Normal cycle range and irregularity context.
- Female reproductive cycle review (Peer-reviewed reproductive endocrinology references) — Follicular, ovulatory, and luteal phase background.
Frequently Asked Questions
The menstrual cycle has four phases: (1) Menstruation (bleeding, days 1–5), (2) Follicular phase (days 1–13, overlaps menstruation), during which estrogen rises and follicles develop, (3) Ovulation (about day 14), when the egg is released, and (4) Luteal phase (days 15–28), when progesterone rises to prepare for potential implantation. The total cycle length and phase durations vary between individuals, with 21-35 days considered normal for adults.
A cycle is considered irregular if it varies by more than 7–9 days from cycle to cycle, is consistently shorter than 21 days or longer than 35 days, or if you skip periods entirely. Occasional variation is normal, but persistent irregularity may indicate PCOS, thyroid disease, or other hormonal conditions.
PMS is caused by hormonal fluctuations during the luteal phase, particularly the drop in progesterone and estrogen before menstruation. Serotonin levels also fluctuate with these hormonal changes, contributing to mood symptoms. About 75% of women experience some PMS symptoms, with 3–8% having severe symptoms (PMDD).
Yes. Teenagers often have longer, more irregular cycles (up to 45 days). Cycles become more regular in the 20s and 30s, averaging 28 days. In the late 30s and 40s, cycles may shorten slightly before becoming irregular again during perimenopause. The typical cycle length decreases by about 1 day per decade.
Absolutely. Exercise during menstruation is safe and may actually help reduce cramps, bloating, and mood symptoms through endorphin release. Light to moderate exercise like walking, yoga, or swimming is well-tolerated. Some athletes adjust training intensity by cycle phase, with higher-intensity training during the follicular phase.
Hormonal birth control (pills, patches, IUDs) alters natural cycle patterns. Combined oral contraceptives suppress ovulation entirely, creating an artificial 28-day cycle. After stopping hormonal contraception, it may take 1–3 months for natural cycles to resume. This calculator is designed for natural (non-hormonally-controlled) cycles.
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