Ovulation Calculator
Estimate an ovulation date, fertile window and next expected period from the first day of the last menstrual period and average cycle length.
Enter your values
Change any assumption and calculate again to compare results.
How the date estimate works
In a simple calendar model, ovulation is estimated about 14 days before the next menstrual period. For a 28-day cycle, that places ovulation near cycle day 14. For a 32-day cycle, the estimate moves to around day 18.
The calculator adds cycle length minus 14 days to the first day of the last period. It then shows an approximate fertile window spanning the five days before ovulation through about one day after.
Why actual ovulation can differ
Cycles are not always identical, and the luteal phase is not exactly 14 days for every person. Stress, illness, travel, postpartum changes, perimenopause, polycystic ovary syndrome and many other factors can shift ovulation.
Calendar estimates are therefore less reliable when cycles are irregular. Ovulation predictor kits, cervical-mucus changes, basal-body-temperature tracking or clinical monitoring can provide additional information.
Pregnancy and contraception caution
This calculator cannot confirm ovulation and should not be used as the only method to avoid pregnancy. Sperm can survive for several days and ovulation timing can move unexpectedly.
If you are trying to conceive or need reliable contraception, consider guidance from a qualified healthcare professional.
Important information
This calculator is for general education and planning. It is not a diagnosis, medical device or substitute for individualized healthcare advice. Measurements and formula estimates can differ from clinical assessments.
If the result could affect treatment, pregnancy care, medication, driving, military status or another safety-sensitive decision, confirm it with the appropriate qualified professional or official process.
Frequently Asked Questions
When is ovulation in a 28-day cycle?
A simple calendar estimate places it around day 14, but real timing can vary.
How is the fertile window estimated?
The calculator shows roughly five days before the estimated ovulation date through one day after.
Can I use this with irregular cycles?
You can enter an average cycle length, but calendar estimates are less reliable when cycle lengths vary substantially.