The simple idea (no memorising)
A typical cycle runs about 21–35 days, with roughly 2–7 days of bleeding. But here's the trick that makes cycles predictable:
- the luteal phase (after ovulation) is almost always about 14 days;
- the follicular phase (before ovulation) is the part that stretches or shrinks.
So no matter how long the whole cycle is, *ovulation happens about 14 days before the next period* — count backwards, not forwards.
| Cycle length | Ovulation is roughly on day… |
|---|---|
| 28 days | day 14 |
| 30 days | day 16 |
| 35 days | day 21 |
The cervix leaves clues
The cervix produces mucus that changes with the hormones:
- around ovulation, estrogen makes it thin, clear and stretchy — like raw egg‑white — so sperm can swim through easily;
- after ovulation, progesterone makes it thick and sticky, a barrier that keeps sperm out.
So "egg‑white" mucus is nature's own fertile‑window signal.
Why it matters
This is the practical heart of fertility. Couples trying to conceive aim for the days around ovulation; the same knowledge underlies natural family planning. And when you later investigate infertility, you'll time tests by this same logic — mid‑luteal, about a week before the expected period, not rigidly "day 21."
Quick check ✅
- Which half of the cycle is fixed in length, and roughly how long is it?
- What does fertile, estrogen‑driven cervical mucus look and feel like?
Remember this 🌟
Where we're going next → What happens to the whole rhythm when ovulation simply doesn't occur? Concept 14.