For many women, monthly menstrual cycles are very predictable, allowing them to easily track and know when to expect their monthly period. When they decide they want to have a baby, a few simple calculations can help them figure out the most fertile times to try to conceive. The technique also works in reverse, and they can estimate the best times to avoid intercourse if birth control isn’t an option.
While it’s not possible to guarantee you can pinpoint your most fertile days for conception every month, some real science is behind the method used to calculate a best guess. Whether you want to conceive — or add an extra layer of protection to your birth control method — start by using these tips to calculate when you could become pregnant.
Length of Your Menstrual Cycle
Your menstrual cycle begins on the first day of your period and is a critical component in determining when you can get pregnant. Most women have a 28-day cycle from the first day of one period to the first day of the next, but it can vary. Some have cycles as short as 21 days, for example. Technically, your cycle is considered regular if you have your period at least every 24 to 38 days, but that degree of variation can make estimating your fertility period challenging.
If you skip periods entirely or have cycle lengths that fall outside the “regular” range or change significantly from month-to-month, then you have what is known as an irregular cycle. Unfortunately, that will make it harder to pinpoint when you are likely to ovulate. If you are having difficulty conceiving and want to calculate the best estimate for when you could become pregnant, you may have to track your periods for a few months to determine an average length or some sense of a pattern for your cycle.
Tracking Your Ovulation
Ovulation occurs when one of the ovaries in your body releases an egg, a critical process for fertilization and pregnancy. The exact time of ovulation is impossible to predict without tests, but it typically occurs near the middle of a standard 28-day cycle. If the released egg isn’t fertilized, then your period will start anywhere from 10 to 16 days (on average) after ovulation.
Calculating from the beginning of your last period, if you typically have a regular 28-day cycle, you are most likely to ovulate about 14 days after your period starts. If you typically have shorter periods with 21-day cycles, then you are likely to ovulate sooner and could potentially become pregnant immediately after your period.
Sperm from intercourse can live in a woman’s body for as long as five days, but the egg only survives for up to 24 hours after ovulation, which creates a limited time for conception. Generally, the most fertile period extends from about three days before ovulation to about a day after the egg is released.
Signs You Are Ovulating
Counting off days to estimate ovulation is a process that works well for women who have regular menstrual cycles, but the process is much more challenging if their periods are irregular. For women who can’t rely on predictability in their monthly cycles, the frustration begins with trying to pinpoint when they will have their period and ends with calculating when they are likely to ovulate — all while knowing the estimates could end up being meaningless if their period falls at a dramatically different time than the previous month.
Fortunately, other physical signs of ovulation are often present to help you pinpoint when your body is preparing to release an egg. Vaginal discharge or mucus around this time is thinner, clearer and more slippery to help sperm move more efficiently through the reproductive tract. You may experience cramping on one side around the time you ovulate, but this is not true for every woman.
Your basal temperature — body temperature when you first wake up but before you get out of bed and start moving around — may be slightly elevated around the time of ovulation. You may need to track this reading for a few months to confirm your pattern. Over-the-counter ovulation predictors have also helped many women determine their estimated ovulation dates. If you’re working with a doctor, he or she may test for LH (luteinizing hormone) levels, which start climbing about 36 hours before ovulation and peak at about 12 hours before.
When You Don't Ovulate
Even women with the most consistent menstrual cycles can suddenly skip their period, which most likely means they didn’t ovulate. The reason is usually something simple like experiencing higher than normal stress, but a missed period could also have a medical reason. The most obvious medical reason is pregnancy, and testing for it is quick and easy. Women who recently had babies and are still breastfeeding also don’t usually ovulate — although they could, so birth control is still important.
If you are nearing 50 years of age, you could be experiencing perimenopause symptoms, which include irregular ovulation and periods. Certain types of birth control, such as intrauterine devices (IUDs), can also affect ovulation and periods, as can low body weight, particularly low body weight related to an eating disorder like anorexia nervosa. Serious medical conditions are less likely but possible and could include polycystic ovary syndrome, pelvic inflammatory disease and premature ovarian failure.
Planning for Conception
If conception is not your goal, it’s important to remember that sperm can live inside the female reproductive organs for up to five days — some experts say it’s closer to seven — which makes birth control important at all times, even when you’re on your period. This is particularly true for women with 21-day or irregular menstrual cycles, but all women should be aware of the possibility of ovulation at an unexpected time.
If conception is your goal, you can try to increase your chance of conception in a few ways. Frequent intercourse is an obvious simple answer but not always practical for various reasons. Studies have shown no difference in pregnancy rates for couples who had sex every day versus every other day, and every other day is more natural and relaxed for most couples, which can be beneficial at a time when stress can impede the process.
Try to relax and let go of any stress, particularly related to conception. A woman who stresses or worries too much may have an irregular cycle, which can disrupt ovulation and fertility. After having intercourse, stay in bed for at least 15 minutes after to relax and increase the chance of fertilizing the egg. Also, before you begin trying to conceive, have a preconception checkup and physical to make sure your body is healthy and prepared for pregnancy.
Pre-Pregnancy Habits and Your Health
Practicing healthy pre-pregnancy habits will increase your chance of enjoying a healthy pregnancy and a healthy baby. If you have bad health habits, the time to change them is before you conceive. Quit smoking and completely quit or curtail drinking alcohol. Get plenty of exercise and try to get your body mass index (BMI) in a normal range. Start taking a prenatal vitamin loaded with folic acid and discuss any supplements or medications you take with your doctor. If you have a medical condition, make sure pregnancy won’t be a problem.
If you have tracked your periods to predict your ovulation schedule and/or used an ovulation predictor and you have frequent intercourse, then it may be time to speak to your OB/GYN if you haven’t conceived. Both women and men can be evaluated for fertility issues. If you or your partner is infertile, many treatments and other options are available to help you expand your family.
Your doctor may refer you to a fertility specialist to discuss treatment options such as fertility drugs to increase egg or sperm production, surgery to repair damaged organs, artificial insemination and other forms of assisted reproduction. You may also want to discuss non-medical options like adoption.