Menstrual Period & Ovulation Cycle Calculator
Forecast future period dates, project the four physiological cycle phases, and evaluate menstrual regularity with clinical FIGO standards.
Current Cycle Inputs
Cycle History (Optional)
Current Day
Day 4
Next Menstruation Starts
In 24 days
Predicted: July 7, 2026
Regularity Assessment
Insufficient Data
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Phase Symptom Tracker & Lifestyle Tips
Menstruation Phase (Days 1 - 5)
Typical symptoms: Menstrual cramping, fatigue, back pain, and lower physical energy levels.
Predicted Menstrual Cycles (12-Month Ledger)
| Cycle # | Period Duration | Predicted Ovulation | Fertile Window | PMS Window |
|---|---|---|---|---|
| Cycle 1 | July 7 – July 11 | July 21, 2026 | July 16 – July 21 | July 25 – August 3 |
| Cycle 2 | August 4 – August 8 | August 18, 2026 | August 13 – August 18 | August 22 – August 31 |
| Cycle 3 | September 1 – September 5 | September 15, 2026 | September 10 – September 15 | September 19 – September 28 |
| Cycle 4 | September 29 – October 3 | October 13, 2026 | October 8 – October 13 | October 17 – October 26 |
| Cycle 5 | October 27 – October 31 | November 10, 2026 | November 5 – November 10 | November 14 – November 23 |
| Cycle 6 | November 24 – November 28 | December 8, 2026 | December 3 – December 8 | December 12 – December 21 |
| Cycle 7 | December 22 – December 26 | January 5, 2027 | December 31 – January 5 | January 9 – January 18 |
| Cycle 8 | January 19 – January 23 | February 2, 2027 | January 28 – February 2 | February 6 – February 15 |
| Cycle 9 | February 16 – February 20 | March 2, 2027 | February 25 – March 2 | March 6 – March 15 |
| Cycle 10 | March 16 – March 20 | March 30, 2027 | March 25 – March 30 | April 3 – April 12 |
| Cycle 11 | April 13 – April 17 | April 27, 2027 | April 22 – April 27 | May 1 – May 10 |
| Cycle 12 | May 11 – May 15 | May 25, 2027 | May 20 – May 25 | May 29 – June 7 |
Gynecological Endocrinology & The Four Cycle Phases
Understanding the hormonal orchestration of the hypothalamic-pituitary-ovarian (HPO) axis
The human menstrual cycle is a rhythmic biological sequence coordinated by neuroendocrine feedback loops between the hypothalamus (GnRH), the anterior pituitary gland (FSH and LH), and the ovaries (estradiol, progesterone, and inhibin).
According to clinical overviews on the Wikipedia summary on the Menstrual Cycle, a typical reproductive cycle averages 28 days (with a normal FIGO physiological window of 24 to 38 days) and progresses sequentially through four distinct hormonal and anatomical phases:
| Cycle Phase | Nominal Timeline | Dominant Endocrine Regulators | Endometrial & Ovarian Dynamics |
|---|---|---|---|
| 1. Menstruation | Days 1 – 5 | Low Estradiol & Progesterone withdrawal | Ischemic shedding of the stratum functionalis; basal layer preserved |
| 2. Follicular / Proliferative | Days 6 – 13 | Rising Pituitary FSH & Ovarian 17-β Estradiol | Graafian follicle selection; rapid mitotic thickening of the uterine lining |
| 3. Ovulation Phase | Day 14 (Mid-Cycle) | Pituitary LH Surge (> 20–40 mIU/mL) | Follicular rupture; release of secondary oocyte into the fallopian tube |
| 4. Luteal / Secretory | Days 15 – 28 | Corpus Luteum Progesterone & Estradiol | Glandular glycogen secretion; vascular spiral arteriole development |
Gynecological & Hormonal Frequently Asked Questions
Rigorous medical answers regarding menstrual cycles, ovulation timing, and regularity standards
How does the calculator predict upcoming period dates and cycle phases?
The calculator maps consecutive menstrual cycles by adding your mean cycle length to the start date of your last menstrual period (LMP). It computes the four endocrine phases—menstruation, follicular proliferation, mid-cycle ovulation, and secretory luteal phase—by anchoring ovulation exactly 14 days prior to each projected onset.
What constitutes a normal menstrual cycle length according to FIGO standards?
The International Federation of Gynecology and Obstetrics (FIGO) defines a normal adult menstrual cycle length as between 24 and 38 days. Cycle regularity is clinically normal when cycle-to-cycle variation (standard deviation) remains under 7 to 9 days across a 12-month period.
Why is the post-ovulatory luteal phase more consistent than the follicular phase?
Follicular phase duration depends on the variable speed of ovarian follicular recruitment and estrogen production under pituitary FSH. In contrast, the post-ovulatory luteal phase is dictated by the finite, programmed functional lifespan of the corpus luteum, which degrades via luteolysis in exactly 12 to 14 days unless human chorionic gonadotropin (hCG) rescues it.
What physiological endocrine shifts trigger Premenstrual Syndrome (PMS)?
In the late luteal phase (5 to 7 days prior to menses), the regression of the corpus luteum causes a precipitous drop in circulating progesterone and estradiol. This hormonal withdrawal modulates central neurotransmitters—particularly reducing serotonin and GABAergic transmission—giving rise to premenstrual affective symptoms, fluid retention, and physical lethargy.