Ovulation Calculator – Know Your Most Fertile Days to Get Pregnant

Determine the most fertile days to improve your chances of conception. By using our ovulation calculator, know your fertile window based on the last menstrual period and average cycle length.

Enter the First Day of Your Last Menstrual Period:

Average cycle length:

What Is Ovulation?

Ovulation is the process wherein the ovary releases a mature egg during every menstrual cycle. The egg moves into the fallopian tube and waits for the sperm to fertilize it. 

If it is fertilized, it travels to the uterus and implants itself to develop into a pregnancy. If it is left unfertilized, the egg, along with the uterine lining, is shed during the menstrual period. 

Ovulation is the most fertile stage of a menstrual cycle and is therefore essential for you to know about the ovulation days to conceive or avoid pregnancy.

When Do You Ovulate?

Ovulation is likely to happen on the 14th day if you have a typical 28-day menstrual cycle (1). However, this varies from woman to woman because not everyone has a 28-day cycle. 

Tracking your menstrual cycle for at least three months will help you identify the ovulation day. You can either use a calculator or look for  signs and symptoms of ovulation

When Are You Most Fertile?

You are most fertile three days before ovulation, and on the ovulation day itself. In an average 28-day cycle, there are six days (referred to as fertile window) when you have the highest chances of getting pregnant. These are five days before ovulation, and the ovulation day itself. 

It is counted from five days before ovulation because sperm can survive in the woman’s body for three to five days. Having intercourse around this time keeps you at the highest probability of getting pregnant since the sperm waits for the egg in the fallopian tube (2). 

How Long Do You Ovulate?

Ovulation lasts for 12 to 24 hours, the time when the egg is available for fertilization.

The process starts when the body releases follicle-stimulating hormone (FSH) around the 6th to 14th day of the menstrual cycle. This hormone stimulates the ovary to produce follicles where each follicle houses one immature egg. 

Ovulation is triggered by the surge in luteinizing hormone (LH). It usually occurs around 10 to 12 hours after the LH levels reach the peak (3).

How Do You Know You Are Ovulating?

You will experience some subtle changes in your body. However, you may identify these symptoms only if you track the pattern for consecutive months. You might be ovulating when there is:

  • Pain or mild cramping in the lower abdomen (referred to as mittelschmerz)

  • A slight increase in basal body temperature

  • Tenderness in breasts

  • Increased libido

  • Clear and stretchy vaginal discharge

Not every woman will have these symptoms. A better way to track your ovulation is through a calculator.

Track Your Ovulation Using MomJunction's Ovulation Calculator

There is no foolproof method to predict the fertility window and ovulation day, as it is unique to each woman.

The momjunction ovulation calculator gives you the tentative dates of your fertility window when you type in your LMP (last menstrual period) and average cycle length.

It will help you know the most fertile days, ovulation date and fertility calendar for 6 consecutive months.

For a better understanding, have a look at the below table (4).

Monthly Cycle

Fertile Window

Day of Ovulation

Better Fertile Time

35 days

17 to 24 days

21st day

Days 19, 20 and 21

32 days

14 to 21 days

18th day

Days 16, 17 and 18

28 days

10 to 17 days

14th day

Days 12, 13 and 14

24 days 

6 to 13 days

10th day

Days 8, 9 and 10

21 days

3 to 10 days

7th day

Days 5,6 and 7

Tracking Ovulation If You Have Irregular Periods

The most accurate way to track ovulation is to take a hormonal blood test or ultrasonography. There are other less-accurate ways you can use at home (5).

  • Ovulation predictor kits, available in drug stores, track ovulation by detecting LH in the urine.

  • Cervical mucus, a substance on your cervix, changes in quantity at various stages of your cycle. During ovulation, the discharge is more than usual.

  • Use a digital thermometer to check your  basal body temperature  as it tends to rise just before you ovulate, and continues to remain high until your next menstrual cycle begins. The thermometer readings are accurate if they are taken from the vagina or rectum. But for this, you need to check your temperature every day for a few months to understand the fluctuations.

  • Fertility monitors track both estrogen and LH hormones and help identify all the six days of the fertile window. But they are expensive.Remember that an ultrasound scan by a gynecologist or radiologist is the best tool to determine ovulation precisely.

How accurate are ovulation calculators?

Ovulation calculators are only based on averages, and therefore cannot be considered to be accurate. Also, the results may not be right if you are not sure about your last menstrual period, or with irregular cycles.  

The calculators can give you an idea about your likely ovulation time. You can combine this with the symptoms of ovulation to know if you are ovulating.

Can You Get Pregnant On Your Period?

The probability of getting pregnant during your period is low, but it cannot be completely ruled out. Having intercourse during the period might not result in pregnancy because ovulation will occur several days later. It means there is no egg available for fertilization.

But if you have a shorter menstrual cycle, then it could be possible. For instance, if your cycle is 21 days, you will be ovulating earlier. The sperm can live three to five days, and when you have intercourse during the end of your period, you are likely to conceive with early ovulation.

Can You Get Pregnant Five Days After Your Period?

There are chances for you to get pregnant five days after your period. In an average 28th day menstrual cycle, your period begins on day one and ends anytime between four and seven. If you add five days to it (remember the sperm’s life span?), it is already the mid-cycle when you ovulate.



  1. Julie E. Holesh and Megan Lord.; Physiology, ovulation; StatPearls Publishing (2019)

  2. Fertility awareness-based methods of family planning; American College of Obstetricians and Gynecologists (2019)

  3. Beverly G Reed and Bruce R Carr; The normal menstrual cycle and the control of ovulation; Endotext

  4. If you want to get pregnant, timing is everything ; Better Health Channel (2018)

  5. Hsiu-Wei Su et al.; Detection of ovulation, a review of currently available methods; Bioeng Transl Med (2017)

  6. WHO; Family planning/contraception methods;

  7. Yohannes Moges Mittiku et al.; Menstrual irregularity and its associated factors among college students in Ethiopia, 2021;; Frontiers in Global Women’s Health

Disclaimer: Our ovulation calculator is not meant to replace the consultation of a healthcare provider. The calculator result totally depends on the inputs you provide. Always consult your doctor for any advice regarding your health.