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Ovulation Calculator
Ovulation day, fertile window and next period for the next six cycles, from your last period and cycle length.
Calculated in your browser – nothing you enter is sent or stored.
Trying to get pregnant? This ovulation calculator predicts your ovulation day and fertile window – the days when sex is most likely to lead to pregnancy – from the first day of your last period and your average cycle length. It also shows your next period, the earliest day to take a pregnancy test and your fertile days for the next six cycles.
How to Use the Ovulation Calculator
- Enter the first day of your last period – the first day of full bleeding, not spotting.
- Enter your average cycle length: the days from the start of one period to the start of the next. Track 3–6 cycles to get a good average.
- Leave the luteal phase at 14 days unless you know yours from ovulation tests or temperature charts.
How Ovulation Is Calculated
The second half of the cycle – the luteal phase, from ovulation to the next period – is fairly constant at about 14 days. So ovulation happens about 14 days before your next period, not always on day 14:
Ovulation day = first day of last period + cycle length − 14.
Example: if your last period started on October 1, 2026 and your cycle is 28 days, you likely ovulate around October 15, your fertile window runs October 10–15, and your next period is due October 29. With a 32-day cycle, ovulation moves to about October 19.
The Fertile Window
Sperm can survive up to 5 days in the reproductive tract, but an egg lives only about 12–24 hours after ovulation. That makes six days fertile: the five days before ovulation and ovulation day itself. The chance of pregnancy is highest from two days before ovulation through ovulation day. Having sex every 1–2 days during the window gives the best odds.
Signs You Are Ovulating
- LH surge: ovulation predictor kits detect the hormone rise 24–36 hours before ovulation.
- Cervical mucus becomes clear, slippery and stretchy, like raw egg white.
- Basal body temperature rises by about 0.5–1°F after ovulation and stays up until your period.
- Some people feel mild one-sided pelvic pain (mittelschmerz) or breast tenderness.
A calendar estimate works best for regular cycles. If your cycles vary by more than a week, combine it with LH tests or temperature tracking.
When to Test and When to See a Doctor
Home pregnancy tests are most reliable from the first day of a missed period. If you got a positive test, the due date calculator estimates when your baby is due. ACOG advises seeing a doctor if you are under 35 and haven't conceived after 12 months of trying, or after 6 months if you are 35 or older – and sooner if your periods are very irregular or absent.
Sources
- ACOG – Trying to get pregnant? Here's when to have sex
- ACOG – Evaluating infertility
- Office on Women's Health (HHS) – Your menstrual cycle
Last reviewed: October 2026 by the ShrinkBee team. Predictions are estimates and must not be used as birth control. This page is for information and is not medical advice.
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