Period Calculator: Next Period, Ovulation & 6-Month Forecast | 2026
When is my next period due? Free period calculator and period and ovulation tracker. Predict your next period date, ovulation, and fertile window. Average menstrual cycle length for 25 year old and any ageโclient-side only, no data sent.
What This Calculator Does & Who It's For
Calculator Purpose & Outputs
- What You'll Get:
Next Period Date: Estimated as first day of last period + average cycle length. Helps with planning and health management. If you enter longest/shortest cycle (irregularity), you see an estimated date range.
Probable Ovulation: Typically ~14 days before your next period. The most fertile window for potential pregnancy.
Fertile Window: ~5 days before ovulation plus the day of ovulation. When conception is most likely.
6-Month Forecast: List of estimated period start dates and an interactive calendar with period days (red), fertile window (light blue), and ovulation (dark blue).
Menopause Context: Definition (12 months without a period) and typical age range (49โ52). This calculator does not predict menopause.
(For educational and planning only. Not for birth control. Not a substitute for medical advice.)
- How It Works:
Next Period: Next Period Start = First day of last period + Average cycle length.
Ovulation: Ovulation Date = Next period start โ 14 days.
Fertile Window: From (Ovulation โ 5 days) through Ovulation (6 calendar days).
Phase definitions: The cycle begins on day 1 of bleeding (Menstrual Phase) and ends just before the next period. Period duration is typically 2โ7 days; average cycle length is usually 21โ45 days (default 28).
- Ideal Users:
Anyone asking "When is my next period due?": Enter first day of last period and average cycle length for a next-period estimate and 6-month forecast.
People tracking average menstrual cycle length: Use your typical cycle length (average menstrual cycle length for 25 year old is often 28โ30 days; use your own for best results).
Period and ovulation tracker users: Get next period date, ovulation, and fertile window in one place with a 6-month visual calendar.
Anyone curious about symptoms of a regular period: See the FAQ for common period symptoms; the calculator focuses on dates and fertility windows.
Privacy: All inputs and results stay on your device; nothing is sent to a server.
- Accuracy & Limitations:Predictions assume a consistent average cycle. Stress, illness, travel, and natural variation can shift your actual period. Irregular cycles reduce accuracy; use the longest/shortest option to see a range. Not for birth control. Pregnancy and breastfeeding stop periodsโthe forecast does not apply then. See a healthcare provider for medical advice.
What Is a Normal Cycle?
Average Menstrual Cycle Length and Regularity
- Cycle Length Range:A normal menstrual cycle is typically 21โ35 days from the first day of one period to the first day of the next. Some sources extend the upper range to 45 days. Average menstrual cycle length for people in their twenties is often around 28โ30 days, but your own average may differ.
- Regular vs Irregular:A cycle is generally considered regular if the variation between your shortest and longest cycle (over the last 6 months) is less than 8 days. So 26-day and 32-day cycles can both be normal; what matters is consistency within your range. This calculator lets you enter longest and shortest cycle to show an estimated date range when you have variation.
- Period Duration:Bleeding typically lasts 2โ7 days. The calculator asks for period duration so the forecast calendar can mark period days correctly. Day 1 of the cycle is the first day of full bleeding (Menstrual Phase).
Life Transitions: Menarche to Menopause
Onset and Conclusion of Menstruation
- Menarche (First Period):The first period usually occurs between ages 12 and 15. Early cycles can be irregular; over time many people settle into a more predictable pattern. You can use this calculator once you have a few cycles to estimate an average length.
- Menopause:Menopause is defined as 12 consecutive months without a period. It usually occurs between ages 49 and 52. Perimenopause (the years before) often brings irregular or skipped cycles. This period calculator does not predict menopauseโsee a healthcare provider for guidance.
- Pregnancy and Breastfeeding:Periods stop during pregnancy and typically do not resume during early breastfeeding (lactational amenorrhea). Can my period stop during pregnancy? Yes. If you think you might be pregnant or are nursing, this forecast may not apply.
Menstrual Phases and Phase Definitions
How the Cycle Is Defined
- Menstrual Phase (Day 1โ~5):Cycle day 1 is the first day of bleeding. The uterus sheds its lining. This phase typically lasts 2โ7 days and is what we mean by "period."
- Follicular Phase:After bleeding ends, follicles in the ovaries develop and estrogen rises. This phase ends at ovulation.
- Ovulation:An egg is released, usually about 14 days before the next period. The fertile window includes the 5 days before ovulation and ovulation day.
- Luteal Phase:After ovulation, the corpus luteum forms and progesterone rises. The cycle ends the day before the next period starts.