ReadingUnderstanding

Getting your fertile window right

Predictions are not birth control

Roughly how a 28-day cycle runs

Period Days 1–5

Follicular Days 6–13

Fertile Days 10–16

Ovulation about day 15

Luteal Days 16–28

What is ovulation?

It is the moment a mature egg is released from an ovary into the fallopian tube. Once released, the egg can only be fertilised for 12 to 24 hours.

Ovulation usually lands about 12 to 13 days before your next period starts. That is an average, though — across people it ranges from 7 to 17 days. This is why counting back from your next period works better than counting forward from your last one.

When is the fertile window?

The days you can get pregnant are the 6 days up to and including ovulation.

• From 5 days before ovulation to the day itself • Sperm can survive up to 5 days inside the body • The egg survives 12 to 24 hours after release

LunaCat shades one extra day after ovulation, so 7 in total. The predicted ovulation day can itself be off by a few days, and the extra day keeps your real fertile window covered.

Signs of ovulation

Knowing the signals your body sends can help.

• Basal body temperature rises about 0.5–1°F (0.3–0.5°C) after ovulation • Cervical mucus turns clear and stretchy, like raw egg white • A light ache low on one side of the abdomen • Sex drive often rises with the hormone shift • Breasts may feel fuller or tender

If an ovulation (LH) test comes back positive, log it. After two of them LunaCat switches from the average to your own ovulation timing.

Why predictions are never exact

The app predicts from the pattern of your past cycles. But the timing of ovulation can move for all sorts of reasons.

• Stress or not enough sleep • Sudden weight change • Travel and time zone shifts • Illness or medication • A change in how much you exercise

It moves more than most people expect. In a study of women whose cycles were reliably 28 days, ovulation still landed anywhere from day 10 to day 22 — and only 1 in 10 ovulated on day 14. Only about 3 in 10 had their whole fertile window inside the often-quoted days 10–17.

Fertile windows are not birth control

Using a fertile window prediction as contraception is not recommended.

• Any app prediction has limits • Ovulation can arrive earlier or later than expected • Because sperm survive up to 5 days, no day can be called reliably "safe"

If you want dependable contraception, talk to a healthcare professional about which method suits you.

If you are trying to conceive

To improve your chances:

• Have sex every other day through the fertile window • The 1 to 2 days before ovulation carry the highest odds • Start taking folic acid ahead of time • Keep sleep, food, and routine reasonably steady

If you have been trying without contraception and it has not happened, the usual advice is to get checked after 12 months if you are under 35, or 6 months if you are 35 or older. Go sooner if you are over 40 or your cycles are very irregular.

A fertile window prediction is not birth control. If you want dependable contraception, talk to a healthcare professional.

Sources

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