Mr Calcu | Easily predict ovulation, fertile days, and your next period—perfect for planning, tracking, and taking charge of your cycle.

Track your cycle, predict ovulation, and plan fertility with ease. Empower your health journey and take control of your reproductive timeline now.

Menstrual Cycle Predictor

Last Period Start Date

Average Cycle Length (21-35 days)

* This is an educational tool only. Consult a healthcare provider for medical advice

Cycle Phase Predictor Guidelines

You're just a few clicks away from better cycle clarity.

How to Use This Calculator

Enter the first day of your most recent period.
Enter your average cycle length (in days).
View predicted ovulation date, fertile window, and next period.

When to Use

Tracking menstrual health
Fertility planning and conception
Understanding hormonal rhythms

Who Should Use with Caution

Short Cycles (<24 days): Ovulation may occur as early as Day 7–9.
Long Cycles (e.g., PCOS): Ovulation is less predictable. Use with LH test confirmation.
Postpartum: Cycle predictions may be unreliable until menstruation returns consistently.
Perimenopausal Users: Hormonal changes can disrupt ovulation timing.
After Stopping Birth Control: It may take several cycles for ovulation to stabilize.

For best results, use this tool alongside ovulation predictor kits, cervical mucus observation, or basal body temperature monitoring.

Cycle Phase Predictor Description

Menstrual Cycle Overview

The menstrual cycle consists of four primary phases, regulated by complex hormonal interactions:

Menstruation – Shedding of the uterine lining, lasting 3–7 days.
Follicular Phase – Begins on the first day of menstruation and continues until ovulation. Estrogen rises, and FSH stimulates follicle growth.
Ovulation – Triggered by an LH surge. The mature egg is released, marking peak fertility.
Luteal Phase – Progesterone increases to support possible implantation. This phase typically lasts ~14 days.

Hormonal Control

The menstrual cycle is regulated by the hypothalamic–pituitary–gonadal (HPG) axis:

Hypothalamus – Releases GnRH.
Pituitary Gland – Secretes LH and FSH.
Ovaries – Produce estrogen and progesterone in response.

Cycle Timing

Cycle Length: 21–35 days.
Follicular Phase: Variable duration.
Luteal Phase: More constant (~14 days).
Ovulation Timing: ~14 days before the next period.

Key Equations

Next Period Date = Last Period Start Date + Cycle Length
Ovulation Date = Next Period Date - 14
Fertile Window = Ovulation Date ± 2 days
Follicular Phase = Cycle Length - 14 (luteal phase)

Example: If Cycle Length = 30 → Ovulation ≈ Day 16 → Fertile Window = Days 14–18

Understanding Biological Variation

Ovulation may vary by ±2 days even in regular cycles.
Data from multiple cycles provides better individual patterns.
External factors like stress, illness, and diet can shift ovulation timing.

Pro Tip: Log at least 6 months of cycle data. Use your average cycle length and standard deviation to calculate a personalized fertile window.

Technical Accuracy

Ensure digital precision when exporting or importing fertility tracking data:

1 MB = 10^6 bytes
1 MiB = 2^20 bytes = 1,048,576 bytes

Health devices and hormone tracking software often mix these units. Use correct labels to avoid data loss or confusion.

Real-World Case Studies

Case Study 1: PCOS Variability

Age: 29
Cycle Lengths: 35–60 days
LH Tests: Ovulation observed on Day 24–30
Outcome: Conception achieved with ovulation on Day 27

Case Study 2: Short Cycle Conception

Age: 25
Cycle Length: 23 days
Calculated Ovulation: Day 9
Fertility Signs: Confirmed by ultrasound on Day 9
Outcome: Conception occurred on Day 8

Start using the Cycle Phase Predictor now to stay in sync with your body and plan your month with confidence!

Example Calculation

Start Date	Cycle Length	Next Period	Ovulation Date	Fertile Window
2023-08-01	28 days	2023-08-29	2023-08-15	2023-08-13 – 17
2023-05-10	32 days	2023-06-11	2023-05-28	2023-05-26 – 30
2023-11-03	26 days	2023-11-29	2023-11-15	2023-11-13 – 17
2023-07-20	38 days	2023-08-27	2023-08-13	2023-08-11 – 15
2023-02-02	21 days	2023-02-23	2023-02-09	2023-02-07 – 11
2023-03-15	23 days	2023-04-07	2023-03-24	2023-03-22 – 26
2023-09-09	60 days	2023-11-08	2023-10-25	2023-10-23 – 27

Frequently Asked Questions

It's moderately accurate if cycles are consistent. Ovulation typically occurs 14 days before the next period. Tracking several months improves prediction precision. For best results, combine with LH surge tests or BBT.

Yes, but use caution. Irregular cycles introduce greater variability. Track LH, cervical mucus, or use ovulation prediction kits to enhance accuracy. The tool will assume a ±2 day margin from your calculated ovulation date.

Although 14 days is average, luteal phases can range 11–17 days. If you know your specific luteal length (e.g., from hormone tests), adjust the ovulation formula accordingly: Ovulation Date = Next Period Date - Luteal Length.

Yes. Prolactin suppresses ovulation during breastfeeding. Predictions are only valid once regular cycles resume. Ovulation may occur unpredictably in the interim.

Cycle irregularity is common for 1–6 months post-cessation. It’s best to log several natural cycles before relying on predictions.

Use LH test strips or track basal body temperature daily. Cervical mucus changes and ovulation pain can also be supportive indicators.