Understanding your cycle
The four phases
- Menstrual (days ~1–5) — your period.
- Follicular (days ~1–13) — an egg matures; energy often rises.
- Ovulatory (around day 14) — the fertile window.
- Luteal (days ~15–28) — PMS symptoms can appear.
Phase timing is approximate and varies between people; the luteal phase (~12–16 days) is the most consistent. Next period = last period + your cycle length.
⚕️ A prediction for information only, most accurate with regular cycles. It is not a contraceptive method. Speak to your GP about irregular, very heavy or painful periods.
Questions
How do I calculate my next period?
Add your usual cycle length to the first day of your last period. This tool does it and shows the countdown.
What if my cycle is irregular?
Predictions will be rough. Tracking several cycles improves accuracy; persistent irregularity is worth discussing with a GP.
Sources
Evidence-based · last reviewed July 2026