Menstrual Cycle Calculator

Map your entire menstrual cycle with phase dates, biological milestones, and an illustrative reproductive hormone curve.

Generate Your Menstrual Cycle Map

Enter your last period date and typical cycle length.

Calculated on your device. Nothing is saved.

Date bleeding began

days
days
Key Takeaway: Estrogen dominates the follicular phase, building stamina and optimism, while progesterone dominates the luteal phase, supporting restoration and metabolic function.

The Neuroendocrine Feedback System

The menstrual cycle is driven by the Hypothalamic-Pituitary-Ovarian (HPO) axis:

  • GnRH from the hypothalamus stimulates pituitary secretion of FSH and LH.
  • Ovarian follicles respond by producing Estrogen.
  • Peak estrogen triggers the mid-cycle LH surge.
  • Post-ovulation, the corpus luteum produces Progesterone to stabilize the endometrium.

When to See a Doctor

Online calculators provide general estimates based on biological averages. Consult a healthcare provider (such as an OB/GYN or general practitioner) if you notice:

  • Your periods suddenly become irregular after being consistent
  • Your cycle is consistently shorter than 21 days or longer than 35 days
  • Your period bleeding lasts longer than 7 days or is unusually heavy (soaking through a pad/tampon every hour)
  • You experience severe, debilitating pelvic pain or cramping that disrupts daily life
  • You experience bleeding between periods or after intercourse
  • You are under 35 and have been trying to conceive for 12 months (or 6 months if 35+)
  • Your period has stopped completely for 90 days or more (and you are not pregnant)
Next Logical Step

Check Your Phase for Today

See where you are right now on the interactive phase ring.

Open Cycle Phases Calculator

Frequently Asked Questions

Evidence-based answers to common questions about your cycle and fertility.

How do hormones fluctuate during the menstrual cycle?

During the follicular phase, FSH stimulates follicle growth and Estrogen rises. Around mid-cycle, an LH surge triggers ovulation. During the luteal phase, Progesterone rises to support the endometrium, dropping before menstruation begins if pregnancy does not occur.

What is the difference between the menstrual and follicular phases?

The menstrual phase (Days 1–5) refers specifically to active bleeding. The follicular phase begins on Day 1 and continues until ovulation occurs (around Day 14), overlapping with menstruation.

Explore other free, private tools for tracking your menstrual cycle and fertility.

Period & Cycle

Period Cycle Phases Calculator

Find today's menstrual phase, cycle day, and days remaining in each phase with an interactive 4-phase biological cycle ring. Fast and private.

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Period & Cycle

Follicular Phase Calculator

Calculate the estimated start and end dates of your follicular phase, total phase length, and key hormonal changes. Private, client-side tool.

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Period & Cycle

Luteal Phase Calculator

Calculate your luteal phase length from confirmed ovulation to period start. Understand luteal phase defect signs and cycle health.

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Ovulation & Fertility

Ovulation Calculator

Calculate your estimated ovulation date, 6-day fertile window, and peak conception days. 100% private, client-side calculator with zero tracking.

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Medical & Scientific Sources

  1. American College of Obstetricians and Gynecologists (ACOG)(2022). "Your Menstrual Cycle"
  2. Endocrine Society(2022). "Reproductive Hormones and the Menstrual Cycle"
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