Calculate your ovulation date and 6-day fertile window based on your cycle. See the next 3 cycles with peak fertility dates, and understand how to confirm ovulation using LH tests and basal body temperature.
Your Fertile Window
Ovulation Date—
Fertile Window—
Peak Fertility Days—
Next Period Expected—
Next 3 Cycles Forecast
Cycle
Period Start
Fertile Window
Ovulation Date
Next Period
How to Confirm Ovulation
Method
When to Use
Accuracy
Notes
LH Urine Test (OPK)
Start 3–4 days before predicted ovulation
High (detects LH surge 24–36h before)
Most practical; inexpensive strips available
Basal Body Temperature
Every morning before rising
Confirms after ovulation occurred
Temp rises 0.2–0.5°F after ovulation
Cervical Mucus
Daily observation
Moderate
Egg-white consistency = approaching ovulation
Transvaginal Ultrasound
Mid-cycle, with provider
Very high (direct visualization)
Clinical; used in fertility treatment
Fertility Monitor
Beginning of cycle
High (tracks estrogen + LH)
More informative than simple OPK
Understanding Your Fertile Window
The fertile window spans 6 days: the 5 days before ovulation and ovulation day itself. An egg survives only 12–24 hours after release, but sperm can survive 3–5 days in the female reproductive tract — which is why timing intercourse before ovulation is important.
For a 28-day cycle with a 14-day luteal phase: 28 − 14 = Day 14 ovulation
Signs You May Be Ovulating
LH surge on ovulation predictor kit (positive OPK)
Egg-white cervical mucus — clear, stretchy, similar to raw egg white
Mild pelvic pain or cramping on one side (mittelschmerz)
Increased basal body temperature (rises ~0.2–0.5°F after ovulation)
Breast tenderness, increased libido
Frequently Asked Questions
Ovulation typically occurs 12–16 days before your next period. Physical signs include a change in cervical mucus (becoming clear and stretchy like egg whites), a slight rise in basal body temperature (0.2–0.5°C), and sometimes mild one-sided pelvic pain (mittelschmerz). Ovulation predictor kits (OPKs) detect the LH surge that precedes ovulation by 24–36 hours and are the most reliable non-lab method.
Calendar prediction works best with regular 28–30 day cycles. Cycle length variation of even 2–3 days shifts the ovulation estimate by the same amount. Stress, illness, travel, and other factors can delay ovulation unpredictably. For conception planning or avoiding pregnancy, combine calendar prediction with OPKs or BBT tracking for greater reliability.
The egg is viable for fertilization for only 12–24 hours after ovulation. However, the fertile window extends 5–6 days because sperm can survive up to 5 days in the fallopian tubes. This means the best days for conception are the 2–3 days before ovulation and the day of ovulation itself. After ovulation, fertilization is no longer possible until the next cycle.
With a 32-day cycle and a standard 14-day luteal phase, ovulation occurs on cycle day 18 (32 − 14 = 18). If your last period started January 1, ovulation falls around January 18. The fertile window runs January 13–18 (5 days before ovulation through ovulation day). Peak conception probability is January 17–18. Start using LH test strips around January 14 (4 days before predicted ovulation) to catch the LH surge 24–36 hours before ovulation occurs.
The luteal phase is the time between ovulation and the start of the next period, typically 12–16 days. Unlike the follicular phase (which can vary significantly), the luteal phase length is relatively fixed for each individual. A short luteal phase (less than 10 days) can impair implantation because the uterine lining doesn't have time to develop adequately. If you notice your period arrives very soon after a positive OPK, mention this to your provider — it may indicate luteal phase defect.