Health
Ovulation Calculator
Find your fertile window, ovulation date, and next period — with a color-coded cycle calendar and 3-cycle projection.
days
Typical range: 24–38 days
days
Usually 12–16 days (default 14)
Estimated Ovulation Date
Fertile Window
6-day peak fertility period
Peak Fertility Days
2 days before ovulation
Next Period
Days Until Ovulation
Cycle Phase Legend
Menstruation
Follicular
Fertile Window
Ovulation Day
Luteal Phase
Cycle Phase Timeline (Current Cycle)
This calculator uses the standard calendar method (ACOG). Actual ovulation varies with stress, illness, and hormonal changes. For conception or contraception decisions, use ovulation predictor kits (OPKs) or basal body temperature charting in addition to calendar estimates.
How Ovulation Is Calculated
Ovulation is estimated by subtracting the luteal phase length from the total cycle length: Ovulation Day = Cycle Day (Cycle Length − Luteal Phase). For a 28-day cycle with a 14-day luteal phase, ovulation falls on cycle day 14.
The fertile window spans 5 days before ovulation through ovulation day — reflecting sperm survival of up to 5 days (ACOG). Peak fertility is the 2–3 days immediately before ovulation, when the probability of conception is highest.
Cycle phases: Menstruation (days 1–5 average) → Follicular (days 1–ovulation, FSH stimulates follicle growth) → Ovulation (egg release, day 14 for a 28-day cycle) → Luteal (post-ovulation through end of cycle, progesterone peaks).
Frequently Asked Questions
How do I calculate my ovulation date?
Ovulation typically occurs 14 days before your next period. Subtract your luteal phase length (usually 14 days) from your cycle length to find the ovulation cycle day. For a 28-day cycle, that's day 14. According to ACOG, normal cycles range from 24 to 38 days.
What is the fertile window?
The fertile window is the 6-day interval ending on ovulation day — five days before ovulation plus the ovulation day itself. Sperm can survive in the female reproductive tract for up to 5 days. ACOG notes peak fertility is the 2–3 days leading up to ovulation.
How accurate is this ovulation calculator?
This calculator uses the calendar method and is an estimate only. Actual ovulation can shift due to stress, illness, and hormonal changes. For precise tracking, pair this with ovulation predictor kits (OPKs), basal body temperature charting, or cervical mucus monitoring.
What is a normal cycle length?
Per ACOG, a normal menstrual cycle ranges from 24 to 38 days. The average is 28 days, but significant variation is healthy and normal. Cycles shorter than 21 days or longer than 45 days may warrant medical evaluation.
What is the luteal phase?
The luteal phase runs from ovulation to the first day of the next period, typically 12–16 days (most commonly 14 days). Unlike the follicular phase, luteal phase length is relatively consistent between cycles — which is why subtracting it from cycle length reliably estimates ovulation.
Can I get pregnant outside the fertile window?
The probability is very low but not zero. An egg is viable for only 12–24 hours after ovulation. Cycles can vary, shifting the fertile window unexpectedly — which is why calendar-only methods have limited reliability as contraception.
How do irregular cycles affect this calculator?
Irregular cycles (length varying by 7+ days between cycles) make calendar prediction unreliable. ACOG recommends physical sign monitoring — cervical mucus changes, mid-cycle pain, or OPKs — for better accuracy with irregular cycles.
What are the four phases of the menstrual cycle?
(1) Menstruation — uterine lining sheds, days 1–5 average; (2) Follicular phase — FSH stimulates follicle development through ovulation; (3) Ovulation — LH surge triggers egg release; (4) Luteal phase — progesterone peaks to prepare the lining, ovulation through end of cycle.
When should I see a doctor about fertility?
ACOG recommends evaluation if you're under 35 and haven't conceived after 12 months of regular unprotected intercourse, or 35+ after 6 months. Seek earlier evaluation for irregular cycles, PCOS, endometriosis, prior pelvic infections, or two or more miscarriages.
How does this calculator project future cycles?
Each projected cycle starts on the day the prior cycle ends (cycle start + cycle length). All phase dates — menstruation, follicular, fertile window, ovulation, and luteal — are recalculated for each cycle, assuming consistent cycle length and luteal phase.