Ovulation Calculator
Estimate your ovulation date, fertile window, and next period based on your cycle length and last menstrual period.
Fertile Window
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Upcoming cycle dates
3-cycle forecast
Assumes ovulation 14 days before the next period. Cycles vary — this is an estimate only.
What is Ovulation Calculator?
The Ovulation Calculator estimates your ovulation date, fertile window, and next period based on the first day of your last menstrual period and your average cycle length. It also provides a 3-cycle forecast so you can plan ahead across multiple months.
How to use
- 1 Enter the first day of your last menstrual period using the date picker.
- 2 Set your typical cycle length using the plus and minus buttons (default is 28 days).
- 3 Review your fertile window, peak ovulation date, and next period start date.
- 4 Check the 3-cycle forecast for estimated ovulation dates over the coming months.
Formula
Example calculation
With an LMP of June 1 and a 28-day cycle, ovulation is estimated on June 15 (28 - 14 = 14 days after LMP). The fertile window runs from June 10 to June 16, and the next period is expected on June 29.
Frequently asked questions
When is the best time to conceive?
The fertile window spans roughly 6 days: the 5 days before ovulation and the day of ovulation itself. The highest conception probability occurs in the 1-2 days immediately before ovulation, when sperm can survive to meet the egg.
How does cycle length affect ovulation timing?
Ovulation typically occurs 14 days before the next period, regardless of total cycle length. A woman with a 35-day cycle ovulates around day 21, while someone with a 24-day cycle ovulates around day 10.
Are ovulation calculator results reliable?
This calculator assumes a regular cycle and fixed 14-day luteal phase. Real cycles vary due to stress, illness, travel, and hormonal changes. For precise ovulation tracking, use basal body temperature monitoring or ovulation predictor kits (OPKs) alongside this estimate.
What is the luteal phase?
The luteal phase is the period between ovulation and the start of the next menstrual period. It is typically 12-16 days long (the calculator assumes 14 days). A luteal phase shorter than 10 days may indicate a hormonal issue worth discussing with a doctor.
Can I get pregnant outside the fertile window?
It is unlikely but possible if ovulation is irregular. Sperm can survive in the reproductive tract for up to 5 days, and irregular cycles mean ovulation can occur at unexpected times. If pregnancy is the goal, tracking additional physical signs of ovulation alongside this calculator is recommended.