Ovulation Calculator
Enter the first day of your last period and your cycle length to see the estimated ovulation date, fertile days and next period, also on a monthly calendar.
Note: These calculations are for informational purposes only and do not replace professional tax or financial advice. All information without guarantee.
FAQ
Frequently Asked Questions
When does ovulation occur?
Ovulation typically occurs about 14 days before the next period. With a 28-day cycle, that is around day 14. Fertile days span approximately 5 days before ovulation through 1 day after.
How can I determine my fertile days?
Methods include tracking basal body temperature, observing cervical mucus changes, using ovulation test strips, and calendar-based calculation. Combining methods increases accuracy.
Can I use the ovulation calculator for contraception?
No. The calculator simply places ovulation 14 days before the next expected period and marks the 5 days before to 1 day after as fertile – with a period starting on 1 April and a 28-day cycle, that means ovulation on 15 April and fertile days from 10 to 16 April. If ovulation shifts by a few days, for instance due to stress, illness or travel, the fertile window shifts too, and a calendar calculation cannot detect this. It is therefore not suitable for contraception; ask your gynaecologist for advice.
Guide
What is the Ovulation Calculator?
The ovulation calculator determines the fertile days and expected ovulation date based on cycle length.
How does the Ovulation Calculator work?
Enter the first day of your last period and average cycle length. Ovulation occurs approx. 14 days before the next period. The fertile window is about 5 days before to 1 day after ovulation.
Key Data and Facts
Ovulation: approx. 14 days before next period. Fertile days: 5-6 days per cycle. Average cycle length: 28 days (21-35 normal). Sperm survive up to 5 days.
Step-by-Step Guide
How to calculate your ovulation and fertile days step by step: 1. Enter the first day of your last period: Note the date on which your last menstruation began. 2. Specify the average cycle length: Count the days from the first day of one period to the day before the next period. The average over 3-6 cycles is the most reliable. Normal is 21-35 days, with an average of 28 days. 3. Calculate ovulation: Ovulation usually takes place 12-16 days (on average 14 days) before the next expected period. Ovulation = next expected period minus 14 days. 4. Determine the fertile window: Sperm survive up to 5 days in the body, the egg about 12-24 hours. The fertile days therefore range from 5 days before to 1 day after ovulation. 5. Note: The calculator provides estimates. Irregular cycles make the calculation less accurate.
Calculation Example
Last period: 1 April, cycle length 28 days. Next period: 29 April. Ovulation: around 15 April. Fertile days: 10-16 April.
Sources
Official sources
Calculations are based on applicable German laws and official data:
Full methodology at Methodology.
Reviewed by Konstantin Iakovlev · Last updated:
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