Understanding Your Fertile Window and Ovulation

When is ovulation day?

Ovulation is the day an egg is released, and it typically happens about 14 days before your next period starts. With a 28-day cycle that's around day 14; with a 32-day cycle, around day 18.

The key insight: ovulation is counted backwards from the next period. So the better your next-period prediction, the better your ovulation estimate.

Why the fertile window is about 6 days

An egg survives roughly 24 hours after ovulation, but sperm can survive up to 5 days inside the body. That means pregnancy is possible from about 5 days before ovulation through the day after — a window of roughly 6–7 days.

This is the fertile window. If you're trying to conceive, the 2–3 days right before ovulation matter most.

What if every cycle is a little different?

Real cycles aren't clockwork. Stress, sleep, and travel can shift them by days, which is why a fixed "ovulation is always day 14" rule often misses.

Petal predicts your next period using a weighted average that favors recent cycles. If your cycles trend longer or shorter, the prediction moves with them — and the ovulation and fertile-window markers adjust too.

The honest limits of calendar prediction

Calendar-based estimates are exactly that — estimates. Ovulation can come days earlier or later than predicted, and a day outside the marked window is never a guaranteed 0% chance.

If avoiding pregnancy is your goal, don't rely on calendar predictions alone — discuss contraception with a healthcare professional. Petal says the same thing inside the app, because an honest tool is a better tool.

How to read it on the calendar

Petal color-codes every day of your cycle.

• Red days — logged period days. Light pink marks the predicted next period.
• Yellow days — your fertile window, with the darkest yellow marking estimated ovulation day.
• The home screen adds a daily pregnancy-chance status, worded to match your goal mode: track, conceive, or avoid.