When will I ovulate?

How the date is worked out

Ovulation happens a fairly steady number of days before your next period, usually 12 to 14. That stretch is called the luteal phase. The days before ovulation are what change from cycle to cycle and person to person, which is why a 35-day cycle ovulates much later than a 25-day one.

So the calculator counts forward one cycle length to your next period, then back one luteal phase to ovulation. The fertile window is that day and the five before it.

For example, a period starting Nov 2 in a 31-day cycle puts the next period around Dec 3 and ovulation around Nov 19, with the fertile window Nov 14 to 19.

Why the range matters

Most calculators give you one date. Bodies aren't that precise. Ovulation can move a day or two even in a very regular cycle, and if your cycles vary by more than a few days, the real window can be well outside the single date you were given.

The range here shows that honestly: the likely day, and how early or late it could reasonably fall. If your cycles vary a lot, the fertile window calculator for irregular cycles works from your shortest and longest cycles instead.

Making it more accurate

Two things narrow the estimate. The first is your own history: once you've logged a few periods, the typical length and how much it moves come from you, not an average. The second is ovulation tests. The first positive test in a cycle shows when you actually ovulated, and the gap from there to your next period is your real luteal phase.

CycleHelm Pro does both for you as you log, and sends a short heads-up two days before your window is likely to open.

When to talk to a clinician

Check in if your cycles are usually shorter than 21 days or longer than 35, if they vary by more than a week or so, or if your periods stop for three months and you're not pregnant. If you're trying to conceive, the usual advice is to see someone after a year of trying under 35, after six months at 35 or over, and straight away over 40.