Period Calculator
12-Month Menstrual & Hormonal Planner
Period Calculator
Predict upcoming menstrual period dates, model endocrine cycle phases, and check cycle regularity with historical standard deviation.
Scenarios:
Current Cycle Inputs
days
days
Cycle History (Optional)
Requires at least 3 cycle values to evaluate standard deviation.
Current Day
Day 24
Luteal Phase
Next Menstruation Starts
In 4 days
Predicted: July 7, 2026
Regularity Assessment
Insufficient Data
Provide history logs to evaluate
MenstruationFollicularOvulationLuteal
Phase Symptom Tracker & Lifestyle Tips
Luteal Phase (Days 15 - 28)
Typical symptoms: Progesterone rises and then falls. PMS symptoms (bloating, breast tenderness), mood shifts, and declining physical stamina.
💡 Action tip: Support your body with magnesium-rich foods, moderate aerobic routines, and reduce caffeine.
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 |
Frequently Asked Questions
How does the calculator determine cycle regularity?▾
When you log your previous cycle lengths, the calculator computes the standard deviation. A standard deviation under 2 days represents a highly regular cycle. Ratios between 2 and 4 days indicate moderate regularity. A standard deviation exceeding 4 days signals irregular ovulation intervals, which should be logged for clinical evaluation.
What are the four phases of the menstrual cycle?▾
The cycle has four core phases: 1) Menstruation Phase (active bleeding), 2) Follicular Phase (estrogen rises, preparing eggs), 3) Ovulation Day (release of the mature egg), and 4) Luteal Phase (progesterone spikes to prepare vascular linings for possible conception).
When does PMS start, and what causes it?▾
Premenstrual Syndrome (PMS) typically begins during the latter half of the Luteal Phase (about 5 to 10 days before bleeding start). It is triggered by the sharp decline in estrogen and progesterone hormones when conception does not occur, leading to temporary mood swings, bloating, and fatigue.