Ovulation Calculator

This ovulation calculator is a digital tool that estimates a woman's fertile window based on her menstrual cycle data. The ovulation calculator uses the average length of a woman's menstrual cycle and the date of her last period to predict when she is most likely to ovulate. The fertility window is typically defined as the five days leading up to ovulation and the day of ovulation itself. Enter in the simple information below to find out your ovulation window.


An ovulation calculator is an invaluable tool for women who are trying to conceive or those who want to keep track of their menstrual cycles. By understanding when ovulation occurs, women can better plan for pregnancy or avoid it, depending on their goals. Understanding one's fertility window is essential for several reasons. First, it helps couples time intercourse to maximize their chances of conception. Sperm can survive in the female reproductive system for up to five days, so having intercourse within the fertility window increases the likelihood that sperm will be present when the egg is released. Second, tracking ovulation can help women identify any irregularities in their menstrual cycles, which could signal an underlying health issue. Finally, for those trying to avoid pregnancy, knowing one's fertile window can help determine the best times to abstain from intercourse or use contraception.

Steps to working out when ovulation will occur:

  1. Determine the average length of your menstrual cycle: To use an ovulation calculator effectively, you'll need to know the average duration of your menstrual cycle. To do this, track the number of days between the first day of your period and the day before your next period starts. Record this information for a few months to get an accurate average.
  2. Note the date of your last menstrual period (LMP): The first day of your last menstrual period is a crucial data point for ovulation calculators. Ensure you accurately record this date to get the most precise prediction of your fertile window.
  3. Input your data into the ovulation calculator: Enter your average cycle length and the date of your LMP into the calculator. The tool will then estimate when your next ovulation is likely to occur and provide a range of dates for your fertile window.
  4. Monitor physical signs of ovulation: While ovulation calculators provide an excellent starting point, tracking physical symptoms can further refine your understanding of your fertility window. Common signs of ovulation include changes in basal body temperature, cervical mucus consistency, and mild pelvic pain (mittelschmerz). Using a combination of an ovulation calculator and monitoring physical signs can lead to the most accurate prediction of your fertile window.
  5. Consider using ovulation predictor kits (OPKs): For even greater accuracy, consider using ovulation predictor kits. These over-the-counter tests measure luteinizing hormone (LH) levels in your urine, which surge about 24-48 hours before ovulation. By using OPKs in conjunction with an ovulation calculator, you can pinpoint your fertile window with greater precision.
  6. Maintain a fertility tracker or calendar: Documenting your menstrual cycles, ovulation symptoms, and any relevant data (such as basal body temperature or OPK results) can help you better understand your body's patterns. Over time, this information will enable you to predict your fertility window with increased accuracy.

If you've found a bug, or would like to contact us please click here.

Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.

Copyright © 2019 calculate.co.nz All Rights Reserved. No part of this website, source code, or any of the tools shall be copied, taken or used without the permission of the owner. All calculators and tools on this website are made for educational and indicative use only. Calculate.co.nz is part of the realtor.co.nz, GST Calculator, GST.co.nz, and PAYE Calculator group.