Ovulation Calculator For Irregular Periods

Ovulation Calculator For Irregular Periods
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Free Ovulation Calculator & Calendar (works for irregular periods too!)

When you are trying to conceive, knowing when you are ovulating increases your chance of getting pregnant.

Our free ovulation calculator is a good way to get started. It will help you work out the date when you should next be trying to conceive. You may not always need a fertility monitor, but if you do, our ovulation calculator will also tell you which is best for your individual circumstances if you are looking to get pregnant and take more control of your fertility. If you need help to answer the questions there’s more information below the calculator.

A woman’s menstrual cycle and ovulation

Menstrual cycles vary. The average cycle length is 28 days and around 30% of women ovulate around the middle of their menstrual cycle – meaning 70% of women don’t ovulate regularly in the middle of their menstrual cycle.

Ovulation is the release of an egg from one of the ovaries. Most women are led to believe this usually happens around 14 days after the start of their last period and 14 days before their next menstrual period. However, as stated above for 70% that varies from woman to woman and from one menstrual cycle to the next.

That is why we created this ovulation calculator to help everyone get started with understanding their cycle.

From the data you input, you will instantly receive a full ovulation calendar which includes:

  • Date your next period should begin
  • Dates of your fertility window
  • Your ovulation date

Knowing your most fertile days can increase your chances of getting pregnant significantly.

What’s the difference between ‘regular reproductive cycles’ and ‘irregular reproductive cycles’?

Your ‘cycle’ is the number of days from the start date of your last period to the start date of your next period. If that number of days is about the same from one reproductive cycle to the next (within 1-4 days) and more often than not you have almost no variation in the number of days, then you have ‘regular’ cycles and the average number of cycle days is a useful guideline for the length of your cycles.

If your cycle length varies 5 days or more from one cycle to the next, and particularly if you find that cycles rarely have the same number of days, then you have a degree of ‘irregular’ cycles. Don’t worry though, most women can conceive naturally even if they have irregular cycles, they just need a little more help.

When is the Fertile Window?

Your fertile window is governed by two important factors: how long an egg survives when it’s released from one of your ovaries, and how long sperm can survive in your body.

An egg survives 24-48 hours after you’ve ovulated, while sperm can survive for up to five days in the body. So you have a fertile window of 6-8 fertile days in each cycle when egg and sperm can successfully meet and you can get pregnant.

fertile window

ovusense realtime fertility monitor

If you’re trying to conceive, an ovulation calculator estimates when you’ll be ovulating very well. However, the fastest way to get pregnant whether you have irregular or regular cycles is to use the OvuSense Realtime Fertility Monitor. Unlike any other device, OvuSense is clinically proven to be able to predict ovulation in realtime using current cycle data AND confirm the exact date you ovulated. With this knowledge, you can plan regular sex during your fertile window safe in the knowledge you’re trying at the right time. Learn more about how OvuSense gives you the best chance of getting pregnant.

[1] The key publication outlining the accuracy and positive predictive value of advance prediction of ovulation was shown at the 2014 ESHRE meeting: Papaioannou S, Delkos D, Pardey J (2014).
[2] The accuracy of ovulation confirmation by OvuSense is based on the data set originally published at the 2013 ASRM meeting as a quality index: Papaioannou S, Aslam M (2013), and developed in [1]
[3] Internal Fertility Focus side by side study of OvuFirst and OvuCore Sensors (2021), documented as a class II medical device in the notified body reviewed CE Certificate Technical File.

Ovulation Calculator

Based on the date of your last menstrual period and the length of your typical menstrual cycle, discover which days you’re most likely to be fertile and boost your chance of conceiving.

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All What to Expect content that addresses health or safety is medically reviewed by a team of vetted health professionals. Our Medical Review Board includes OB/GYNs, pediatricians, infectious disease specialists, doulas, lactation counselors, endocrinologists, fertility specialists and more.

We believe you should always know the source of the information you’re reading. Learn more about our editorial and medical review policies.

Latest update:

When to try to get pregnant

Trying to conceive? No one needs to tell you how to do it (leave the diagrams to the amateurs, thank you very much!), but you might need a little help figuring out when is the best time to have sex to get pregnant.

The short answer: The best time to conceive is around the time you ovulate. That prime “getting pregnant” window can include anywhere from a few days before ovulation — because sperm can live to fertilize for three to six days — until about a day after the release of the egg, which is only viable for about 12 to 24 hours.

How we calculate your fertile window

This ovulation calendar estimates when you will ovulate based on the date of your last menstrual cycle and the average number of days between your periods. First, we count back 14 days from the start date of your next expected period to calculate the date you’re most likely to ovulate. Then, we calculate your fertile window, which can extend a few days before ovulation and possibly up to one day after. Just note that this is not an exact science — menstrual cycles can vary from woman to woman and month to month (typical cycle length is anywhere between 21 and 35 days). And, if you have irregular periods, that might make it tougher to pinpoint your fertile window.

Ovulation symptoms

  • Your basal body temperature falls slightly, then rises again when ovulation has taken place.
  • Your cervical mucus becomes clearer and thinner with a more slippery consistency similar to that of egg whites.
  • Your cervix softens and opens up.
  • You may feel a slight twinge of pain or mild cramps in your lower abdomen.
  • Your sex drive may increase.
  • You may notice some light spotting.
  • Your vulva or vagina may appear swollen.

Tips for getting pregnant

Want to up your odds of getting pregnant faster? Here are some tips to try:

1. Take your prenatal vitamin

Start popping that prenatal at least a month before you begin trying for a baby. One study showed that women who were taking their prenatal vitamins while undergoing fertility treatments were twice as likely to get pregnant as those who were only taking a folic acid supplement while going through the same treatments. So while it’s not a guarantee that you’ll hit the baby jackpot sooner, it’s definitely worth a shot!

2. Know the signs of ovulation and time sex around it

Familiarize yourself with the typical ovulation symptoms to look out for and have sex starting a few days before you ovulate, which typically happens midway through your cycle (so on day 14 of a 28-day cycle). Having sex the actual day of ovulation would be ideal, but it can be hard to pinpoint it.

3. Eat well

Eating the right foods and nutrients when you’re trying to conceive can help your dreams of getting pregnant come true more quickly. Make sure you’re incorporating plenty of healthy fats like omega-3s, folate, calcium, protein, iron and fiber into your daily diet.

4. Exercise

Moderate exercise for 30 minutes a day has been shown to boost fertility, so now isn’t the time to turn into a couch potato. Whether it’s hitting the gym, going for a jog or lifting weights, try to fit in some kind of workout while you’re trying to conceive.

5. Don’t worry

Stress can delay ovulation, which in turn will get in the way of conception, and it has also been shown to increase the frequency of uterine contractions, so implantation will be more difficult. Try to find ways to relax: take a yoga class, soak in a bubble bath, go on a rejuvenating walk, write in a journal or get a massage.

6. Get enough sleep

Aim to log in seven to eight solid hours of sleep when you’re trying to conceive. Research has shown that spotty sleep has been linked to irregular periods, which can in turn hinder your fertility. Sleep is also important in staving off stress, which has also been found to hamper baby-making plans.

7. Cut out bad habits

If you smoke, it’s time to quit, as smoking has been shown to have a negative impact on fertility and getting pregnant. It’s also a good idea to stop drinking alcohol (or at least seriously limit your intake) while you’re trying to conceive and cut back your caffeine consumption to no more than 200 milligrams a day (about a 12-ounce cup of coffee).