Ovulation Calculator

Knowing your most fertile days can increase your chances of getting pregnant, and knowing the likelihood of ovulation on a specific day may help you better understand your fertile window. Use our ovulation calculator to see the days you’re most likely to ovulate.

When am I likely to ovulate?

When did your last period start?
E.g., 2019-07-16
Your usual cycle length:
E.g. Cycle typically vary 23 to 35 days
Calculate your due date
likelihood to ovulate this date
Results are based on the information you have provided.
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Start of your last period
  20%
Likelihood to ovulate this day
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Over 99% accurate at detecting the LH surge

Advanced Digital Ovulation testTo accurately identify your fertile days use an ovulation test that detects the changes in your personal fertility hormones in urine. Ovulation tests are 2x more accurate than calendar method3. Clearblue Digital Ovulation Tests are over 99% accurate in detecting the LH surge to identify your most fertile days.


This ovulation calculator is by no means a substitute for knowing what is going on in your body, but rather it should be used for informational purposes only. An ovulation calculator estimates your potential ovulation days by taking your average cycle length and the date of your last period - so it’s basically using the calendar method. An ovulation test measures your personal hormone levels to give you an accurate prediction for the day you ovulate and the days leading up to ovulation.

(X) MYTH: Menstrual cycles are always 28 days long and every woman ovulates on day 14.

(✓)FACT: The average menstrual cycle is 28 days long, but every woman is unique and nearly 50% of women’s cycles vary by 7 days or more1. As menstrual cycles vary in length, so does the timing of ovulation, so it can be difficult to know when YOUR fertile days are.

Understanding your ovulation calculator results

There are many ovulation calculators available today that estimate when your fertile days will occur. These calculators are a form of ‘calendar method’ and work on average data without reading anything about your personal hormone levels.  However, none of us are ‘average’:
1. Cycle lengths vary from woman to woman and cycle to cycle - in fact nearly 50% of menstrual cycles vary by 7 or more days1
2. The timing of ovulation can vary by a few days, even in regular cycles.

Should we have intercourse every day I am fertile?

Professor Bill Ledger

Sperm that are stored within the testicles for too long accumulate damage to the DNA and are less fertile. With couples who have frequent (daily) intercourse, the man will have a lower sperm count per ejaculation but the sperm will be more fertile. If you are trying to conceive then try to have intercourse at least every other day around the time of ovulation.

Why is an ovulation calculator different to a fertility calendar?

An ovulation calculator estimates how likely you are to release an egg on a particular day in your menstrual cycle. A fertility calendar tells you the days on which you’re more likely to conceive if you have sex. 

When an ovary releases an egg this is known as ovulation and this happens once during your menstrual cycle. An ovulation calculator provides an estimate of how likely you are to ovulate on certain days in your cycle and can help you identify your most fertile days. These calculators work by taking the first day of your last period and the length of your menstrual cycle to give a range of days when you may release an egg. 

After an egg is released, it only survives for up to 24 hours, so knowing when you ovulate gives you a very narrow fertility time window for intercourse. The good news is you have more fertile days when you can get pregnant since the chance of conception doesn’t just depend on the lifetime of the egg, but also on the lifetime of the sperm. Sperm can survive in your body for up to 5 days after intercourse, so you can conceive even if you have sex 4 or 5 days before ovulation. Your fertility window is the number of days that the egg and sperm can survive and this is usually around 6 days. 

The 2 most fertile days during this 6-day fertility window are known as peak fertility days. This is the day before ovulation and the day ovulation takes place. An ovulation test measures the surge of luteinising hormone (LH), which happens just 24-36 hours before ovulation, so you can accurately identify your 2 most fertile days.

 

Advanced Digital Ovulation test

 

Use our ovulation calculator to get an approximation for when you ovulate. The more you know about your cycle, the easier it will be to know your fertile window. 

You can get a wider fertility window if you use an ovulation test that also detects estradiol (a form of estrogen). In the days leading up to the LH surge, your estradiol levels will also rise, which then reaches a threshold that triggers the pre-ovulatory LH surge. Tracking your hormones like estradiol and LH will allow you to identify the days of high fertility leading up to ovulation. 

By identifying the additional fertile days before ovulation, you will have more flexibility to plan intercourse around your life and find more opportunity to conceive. This can take the pressure off trying for a baby. 

Other methods of determining when you ovulate, like basal body temperature and the calendar method only inform you that you have already ovulated – after your fertility window closes for that cycle – so are less effective if you want to conceive.

 

What is the difference between ‘ovulation’ and ‘fertile days’?

'Ovulation' is the process of an egg being released from an ovary and this happens 12-16 days before her next period starts.

'Fertile days' are the days during a woman's menstrual cycle, leading up to and including the day of ovulation, when she has the ability to become pregnant if she has unprotected sex.

When are the highest and lowest chances of getting pregnant?

The most fertile days each cycle when you have the best chance of getting pregnant from unprotected sex, are the day of ovulation and the day before – these are the 2 days of ‘peak fertility’. However, due to the fact that sperm can survive for several days in a woman's body during her fertile time there are also a few days before this when you also have an opportunity to get pregnant – these are the days of ‘high fertility’. Outside this ‘fertility window’ of about 6 days, the chances of getting pregnant are low.


Which method is more accurate?

Clearblue Digital Ovulation Tests are over 99% accurate in detecting the LH surge that happens 24-36 hours before ovulation, so they are more accurate than calendar and temperature methods at predicting the most fertile days2.


  1. Creinin MD., et al. Contraception (2004) 70: 289-92
  2. Brezina PR., et al. Fertil & Steril (2011); 95(6): 1867-78
  3. Study of 101 women in the UK comparing a simple calendar method to likelihood of conducting a test on LH surge day (2011).
  4. In a study of 87 women, 4 or more fertile days were identified in 80% of cycles using actual cycle length.

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