Finding your window with a test

A calendar is not enough

In a study of 949 people, calendar methods predicted the day of ovulation with at most 21% accuracy. Roughly one time in five.

Calendar methods assume your cycle is always the same length. Real cycles move from month to month.

That includes LunaCat. It gets better as your logs build up, but anything calculated from a calendar has a ceiling. That is where an ovulation test comes in.

The fertile window is the 6 days ending at ovulation

The fertile window is best described as the 6-day stretch that ends on the day of ovulation. Chances peak within the 2 days before ovulation and drop quickly the day after.

The days before ovulation matter more than the day itself, because sperm can wait a few days.

How an ovulation test works

It measures luteinising hormone (LH) in your urine. That hormone surges just before ovulation. After a positive, ovulation usually follows within 2 days.

About 7% of cycles give a false positive, so do not stake everything on one result. Over a few cycles your own pattern shows up.

How often is best

What the research says

Do not deliberately cut back. Gaps longer than 5 days can lower sperm counts, and a gap of just 2 days is already enough.

A test does not mean «only on that day». It tells you which days to pay extra attention to while keeping a steady rhythm.

Things that do not help

Common beliefs

When to see a doctor

Seek advice after 12 months of trying if you are under 35, and after 6 months if you are 35 or older.

There is no need to rush. About 80% conceive within 6 months, and the first 3 months carry the highest chance. Past 35, the advised waiting time is simply shorter.

Logging it in LunaCat

Log › Ovulation test › Positive

This cycle — the predicted ovulation day moves to that date right away.

From the next cycle — LunaCat measures from your positive to your next period and uses your own luteal length. The textbook number is 13 days, but people range from 7 to 17. Two logs already beat the default by a wide margin.

Not using tests? You can mark ovulation yourself by long-pressing a date in the calendar. A day you mark yourself takes priority over a test result.

This article is for reference. Decisions about your body belong with your doctor.

Every 1–2 days in the fertile window — highest

Two or three times a week — nearly the same

Saving it for «the day» — not advised

Lying down afterwards helps — no evidence

A certain position decides the sex — no evidence

Lubricant makes no difference — some can slow sperm down

Sources

• Optimizing natural fertility: a committee opinion — ASRM, 2022
• Evaluating Infertility — ACOG