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LunWise

Find your fertile days, then confirm them

Calendar estimates are a starting point, not an answer. LunWise estimates your fertile window from your own cycles, then confirms ovulation from LH tests or your waking temperature, and gets more precise every cycle.

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How LunWise helps

  • Fertile window estimates based on your own cycle lengths, not a 28-day default.
  • Log LH tests and LunWise marks your expected ovulation day.
  • Log or import waking temperatures and LunWise confirms ovulation from the temperature rise.
  • Learns your personal luteal phase from confirmed cycles, which sharpens period predictions.
  • A report of cycles and confirmed ovulation dates for fertility appointments.

How the fertile window works

A landmark study found that nearly all pregnancies came from intercourse during a six-day window ending on the day of ovulation. Sperm can survive for several days, but the egg lasts much less time, which is why the days just before ovulation matter most.

LunWise highlights those days plus the day after estimated ovulation, to account for the uncertainty in any estimate.

Estimating versus confirming ovulation

A calendar estimate assumes ovulation happens a set number of days before your next period. That's reasonable on average, but individual cycles vary. LH tests detect the hormone surge that comes shortly before ovulation, and a sustained rise in waking temperature confirms ovulation has happened. LunWise uses both when you log them.

What to log

  • Period start and end dates
  • LH test results: negative, positive or peak
  • Waking temperature, taken before getting up

Questions and answers

How many days is the fertile window?

Research suggests about six days, ending on the day of ovulation. LunWise also highlights the day after estimated ovulation to allow for uncertainty.

Should I use ovulation tests or temperature?

They answer different questions. LH tests warn you ovulation is coming soon. A temperature rise confirms ovulation already happened. Using both gives the clearest picture, and LunWise combines them automatically.

Can I use LunWise as birth control?

No. LunWise is not a contraceptive and its estimates must not be used to prevent pregnancy.

Sources

  1. Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. New England Journal of Medicine, 1995.
  2. Bull JR, Rowland SP, Scherwitzl EB, et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine, 2019.

Last updated October 11, 2026. This page is for general information and isn't medical advice.