Frequently Asked Questions

A period calculator uses the date of your last menstrual period (LMP) and the average length of your cycle to guess when your next period will start. Using standard gynecological formulas, it guesses when your next period will start, when you will ovulate, and when you will be most fertile. By default, most calculators assume a 28-day cycle, but you can change it to fit your own cycle length.

A period calculator is very accurate for women who have regular cycles; it usually predicts the next period within 1 to 3 days. If your cycle length changes because of stress, illness, hormonal changes, or conditions like PCOS, the accuracy may change. For the best results, keep track of your cycle every month for three to six months.

PeriodTracks uses your provided cycle length to estimate future periods and ovulation dates. It is statistically accurate for people with regular cycles. However, cycles naturally vary, and these are estimates — not guarantees. Stress, illness, and hormonal changes can all shift your cycle.

The average length of a menstrual cycle is 28 days, but it can be anywhere from 21 to 35 days. The time between the first day of one period and the first day of the next is what counts. You should talk to your doctor if your cycles are shorter than 21 days or longer than 35 days.

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The fertile window is the five days before ovulation and the day of ovulation itself. Ovulation happens around day 14 of a typical 28-day cycle, so days 10–15 are the most fertile. Sperm can live in the body for up to five days, which gives you a longer time to get pregnant.

The fertile window is the time when pregnancy is most likely. It spans roughly 5 days before ovulation to 1 day after ovulation. Sperm can survive up to 5 days, so intercourse during this window can result in fertilization.

Ovulation usually happens 14 days before your next period is due, not 14 days after your last period. To figure it out, take 14 days off of your average cycle length and count that many days from the start of your last period. For instance, ovulation happens around day 16 of a 30-day cycle.

Ovulation typically occurs about 14 days before your next period starts (the luteal phase). For a 28-day cycle that means around day 14. For shorter or longer cycles, the date shifts accordingly.

The luteal phase is the second half of your menstrual cycle. It starts after ovulation and ends when your next period starts. It usually lasts between 12 and 16 days, and during this time, progesterone levels rise to get the uterus ready for a possible pregnancy. If your luteal phase is less than 10 days, it may be harder to get pregnant and could mean that your hormones are out of balance.

Yes — enter your average cycle length. We recommend tracking several cycles (3–6 months) to find your personal average. For very irregular cycles, please consult a healthcare provider.

Yes, stress is one of the most common reasons why periods are late. When you're under a lot of stress, your body releases cortisol, which can stop the hormones that start ovulation. This can make your period come late, early, or even not at all for a month. You can help your cycle stay regular by managing stress through sleep, exercise, and relaxation.

The luteal phase is the second half of your cycle, from ovulation to the start of your next period. It is typically 12–16 days long and is more consistent than the follicular phase.

Premenstrual syndrome (PMS) is a group of physical and emotional symptoms that happen in the week or two before your period, usually during the luteal phase. Bloating, mood swings, sore breasts, tiredness, and cravings for certain foods are all common symptoms. Most of the time, symptoms go away within a day or two of the start of your period.

There are a lot of things that can change the dates of your period, such as stress, illness, big weight changes, travel, hormonal changes, or starting or stopping birth control. A healthy cycle can change by a few days every month. If your period is always more than a week early or late, you should see a doctor.