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💋 Period Tracker

Track your cycle · Log symptoms · Plan fertility

Quick Preset
Cycle Settings
Irregular cycle
21d45d
3d10d
Tracking Mode

Calendar methods are not a substitute for contraception.

Cycle Wheel
Period
Fertile
Luteal
Hormone Levels (typical cycle)
Estrogen Progesterone Your Day
NEXT PERIOD IN
--d
Follicular Phase
Predicted: —
--
Cycle Day
--
Days to Period
--
Days to Fertile
--
Ovulation Date
Regular
Cycle Type
Low
Conception Chance
Ovulation = Next Period − 14 days
Fertile Window = Ovulation − 5 to Ovulation + 1
Next Period = -- + 28d = --
Fertile: --  •  Ovulation: --
This Month
Period Fertile Ovulation Today

How Period Prediction Works

Next Period Date

Next Period = Last Period Start + Average Cycle Length

The simplest prediction method adds your average cycle length to the first day of your last period. For example, a 28-day cycle starting January 1 predicts January 29 as your next period start date.

Ovulation Window

Ovulation Day ≈ Next Period Start − 14 days

Ovulation typically occurs about 14 days before the start of your next period, based on the luteal phase lasting approximately 14 days in most women.

Fertile Window

Fertile Window = Ovulation Day − 5 to Ovulation Day + 1

The fertile window spans approximately six days: the five days before ovulation (sperm survival) plus ovulation day itself.

About this calculation · Accuracy & Methodology

Key Terms

Menstrual Cycle
The recurring process from the first day of one period to the first day of the next, typically 21–35 days.
Ovulation
The release of an egg from the ovary, usually about 14 days before the next period — the most fertile point of the cycle.
Luteal Phase
From ovulation to menstruation, typically 12–16 days. This phase length is relatively consistent between cycles.
Follicular Phase
From menstruation to ovulation. Its variable length is the primary reason cycle lengths differ between people.
Fertile Window
The ~6-day span when conception is possible, ending the day after ovulation. Sperm can survive up to five days.
Amenorrhea
Absence of menstruation for three or more consecutive cycles. Can be caused by pregnancy, hormonal changes, stress, or medical conditions.

Worked Examples

Regular 28-Day Cycle

Last period: January 1 • Cycle: 28 days

Next Period = Jan 29 • Ovulation = Jan 15 • Fertile: Jan 10–16

Short 24-Day Cycle

Last period: January 1 • Cycle: 24 days

Next Period = Jan 25 • Ovulation = Jan 11 • Fertile: Jan 6–12

Long 35-Day Cycle

Last period: January 1 • Cycle: 35 days

Next Period = Feb 5 • Ovulation = Jan 22 • Fertile: Jan 17–23

Cycle Length Reference Chart

Cycle LengthOvulation Day (approx)Fertile Window StartCycle Type
21 daysDay 7Day 2Short
24 daysDay 10Day 5Short-Normal
28 daysDay 14Day 9Average
30 daysDay 16Day 11Normal
35 daysDay 21Day 16Long

Understanding Your Menstrual Cycle

The menstrual cycle is one of the most important indicators of reproductive health. Tracking your cycle provides valuable insight into your body's patterns and can help you plan ahead, whether trying to conceive, avoid pregnancy, or simply stay informed.

The Four Phases

The menstrual phase (days 1–5 on average) is when the uterine lining sheds. The follicular phase follows, with rising estrogen stimulating follicle growth. Ovulation occurs roughly 14 days before the next period. The luteal phase prepares the uterine lining for potential implantation.

What Affects Regularity

Normal cycles range from 21 to 35 days. Stress, weight changes, intense exercise, age, hormonal contraceptives, and conditions like PCOS can all influence regularity.

When to See a Doctor

Consult a healthcare provider if cycles are consistently shorter than 21 days or longer than 35 days, if you experience bleeding between periods, periods lasting longer than 7 days, or three or more missed periods without pregnancy.

Tips for Accurate Tracking

Record the first day of each period as Day 1. Log symptoms, flow, and secondary signs like temperature shifts. The Cycle Log tab in this tool lets you build a personalized history for more accurate predictions over time.

Frequently Asked Questions

What is considered a normal menstrual cycle length?

A normal cycle ranges from 21 to 35 days, measured from the first day of one period to the first day of the next. The average is 28 days, but only about 15% of women have a textbook 28-day cycle. Cycles that consistently fall outside the 21-35 day range, or that vary by more than 7-9 days from month to month, may warrant a conversation with your healthcare provider.

When is the fertile window in a menstrual cycle?

The fertile window spans approximately 6 days: the 5 days before ovulation and the day of ovulation itself. Sperm can survive in the reproductive tract for up to 5 days, while the egg is viable for only 12-24 hours after release. For a 28-day cycle, ovulation typically occurs around day 14, but this varies significantly. Tracking basal body temperature and cervical mucus improves accuracy over calendar-based prediction alone.

Why is my period irregular?

Common causes of irregular periods include stress, significant weight changes, excessive exercise, polycystic ovary syndrome (PCOS), thyroid disorders, and perimenopause. Cycles are also naturally irregular during the first 2-3 years after menarche and in the years leading up to menopause. If irregularity is new, persistent, or accompanied by heavy bleeding or severe pain, consult a gynecologist to rule out underlying conditions.

How much blood loss during a period is considered normal?

Normal menstrual blood loss is 30-80 mL (about 2-5 tablespoons) over the entire period, lasting 3-7 days. Signs of abnormally heavy bleeding (menorrhagia) include soaking through a pad or tampon every hour for several consecutive hours, passing clots larger than a quarter, or periods lasting longer than 7 days. Heavy menstrual bleeding can lead to iron-deficiency anemia and should be evaluated.

Can stress actually delay or skip a period?

Yes. Psychological and physical stress elevates cortisol, which can suppress gonadotropin-releasing hormone (GnRH) in the hypothalamus. This disrupts the hormonal cascade needed for ovulation, potentially delaying it or preventing it entirely for that cycle. A delayed or skipped period from stress is called functional hypothalamic amenorrhea. Once the stressor resolves, cycles typically return to normal within 1-3 months.