Menstrual Cycle Tracker

How to use the Menstrual Cycle Tracker

1. Enter the first day of your last period and the average length of your cycle.
2. Click Calculate to see your predicted next period, ovulation date, and fertile window.
3. Use Log today to build a history stored in your browser.
4. Export your cycle history to CSV at any time.

How ovulation is estimated

Ovulation typically occurs 14 days before the next period, cycle length − 14 days after the start of the last period. For a 28-day cycle, this is day 14. For a 32-day cycle, it is approximately day 18.

A cycle length between 21 and 35 days is considered normal. Cycles shorter than 21 or longer than 35 days may warrant a discussion with a healthcare provider.

The four cycle phases

• Menstruation (days 1-5 typically), the uterine lining sheds; estrogen and progesterone are at their lowest
• Follicular phase (days 1-13), follicles develop in the ovary; estrogen rises
• Ovulation (around day 14), a mature egg is released; LH surge triggers ovulation
• Luteal phase (days 15-28), progesterone rises to prepare for implantation; if no fertilization, levels drop and the next period begins

Fertile window

The fertile window spans approximately 5 days before ovulation and 1 day after, because sperm can survive up to 5 days in the reproductive tract and the egg is viable for about 24 hours.

Privacy

All data is stored exclusively in your browser's localStorage. Nothing is sent to any server. Clearing your browser data will also delete the cycle history.