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Next period estimate

Period Calculator

Predict your next menstrual cycle.

By Jeff Beem

Updated

Client-side only, cycle data never leaves your device

Phase definition: Cycle day 1 is the first day of bleeding. This tool projects the next period and fertile window from that convention.

01

Cycle baseline

Bleeding length (2–7 days typical).

First day of one period to first day of the next (often 21–45 days).

02

Forecast

Next period (estimated)
Jun 24, 2026

From average cycle length, for planning, not diagnosis.

Probable ovulation

Jun 10, 2026

Often ~14 days before the next period (model).

Fertile window (model)

Jun 5 – Jun 10, 2026

Five days before ovulation through ovulation day, educational only.

Menopause context

Menopause is often framed as 12 months without a period (commonly late 40s–50s). This tool does not predict menopause.

Next six period starts (model)

  • Cycle 2Jun 24, 2026
  • Cycle 3Jul 22, 2026
  • Cycle 4Aug 19, 2026
  • Cycle 5Sep 16, 2026
  • Cycle 6Oct 14, 2026
  • Cycle 7Nov 11, 2026

Six-month calendar (model)

June 2026
SunMonTueWedThuFriSat
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Period Fertile Ovulation

Pregnancy & breastfeeding: Periods stop in pregnancy and often stay absent early in breastfeeding. If that applies, this forecast may not fit, use testing or clinical advice.

Cycle phases (overview)

Menstrual

Day 1 = first bleed; lining sheds; often 2–7 days.

Follicular

Follicles develop; estrogen rises until ovulation.

Ovulation

Egg release; fertile window includes the prior ~5 days plus ovulation day.

Luteal

After ovulation, progesterone rises until the next cycle starts.

Period Calculator: Menstrual Cycle & Reproductive Forecast

Your cycle is more than a calendar number, it's the interval from one period to the next, with natural variation. These insights explain what a normal cycle is, how life stages affect it, and why forecasting helps with planning and health management.

Cycle Intelligence

What Is a Normal Cycle?

Normal isn't one number, it's your pattern.
The "regular if variation is under 8 days" rule helps you know whether to use a single average or a range in the calculator. When your cycles vary, the irregularity option (longest and shortest) gives you a more honest forecast instead of a single date that might be off.

Life Transitions: Onset to Menopause

The calculator is for people who are currently having periods.
Menarche and menopause bookend the years when next-period prediction applies. If you're in perimenopause or your cycles have stopped (pregnancy, breastfeeding, or menopause), the forecast may not apply, see the tool's notes and a healthcare provider when needed.

Why the First Day of Bleeding Matters

That one date drives the whole forecast.
Everything, next period, ovulation, fertile window, is calculated from "first day of last period." Using the real first day of full bleeding (not spotting) keeps the 6-month calendar as accurate as the model allows.

Pregnancy and Breastfeeding

When you're not cycling, a cycle-based forecast doesn't apply.
The tool calls this out so you don't rely on it during pregnancy or early breastfeeding. For those phases, use a pregnancy test or healthcare provider instead.

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 age, client-side only, no data sent.

What This Calculator Does & Who It's For

Calculator Purpose & Outputs

This period calculator answers "When is my next period due?" and works as a period and ovulation tracker. Enter the first day of your last period, period duration, and average menstrual cycle length (e.g. average menstrual cycle length for 25 year old is often 28–30 days; use your own). You get your next period date, probable ovulation, fertile window, and a 6-month forecast with a color-coded calendar. All data stays on your device.
  • 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 (49–52). 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 − 14 days.

    Fertile Window: From (Ovulation − 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 2–7 days; average cycle length is usually 21–45 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 28–30 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 periods, the forecast does not apply then. See a healthcare provider for medical advice.

How the Math Works

The calculator uses straightforward date arithmetic anchored to the first day of your last period (LMP). The next period is projected as LMP + average cycle length. Ovulation is estimated at approximately 14 days before the next period start, based on the standard luteal phase length. The fertile window spans from 5 days before ovulation through ovulation day, six calendar days total, reflecting the lifespan of sperm (up to 5 days) and the egg (about 24 hours). For the 6-month forecast, each subsequent cycle adds the average cycle length to the previous period start date. When you enter longest and shortest recent cycles (for irregular periods), the calculator produces a date range rather than a single date, using both values to bracket the prediction. All dates assume a consistent pattern; stress, illness, and hormonal changes can shift actual timing.

How to Use This Calculator

Select the date your most recent period started, this must be the first day of full bleeding, not spotting, since every calculation anchors to this date. Enter your average period duration (typically 2–7 days) so the forecast calendar can mark bleeding days accurately. Provide your average cycle length in the main field; if your cycle varies, toggle the irregularity option and enter your longest and shortest recent cycles to see a predicted date range instead of a single day. The results show your next period date, probable ovulation day, and fertile window. Scroll down to the 6-month forecast calendar, which color-codes period days in red, the fertile window in light blue, and ovulation in dark blue. This tool is for planning only, it is not a substitute for medical advice or birth control.

What Is a Normal Cycle?

Average Menstrual Cycle Length and Regularity

While 28 days is often cited as the average menstrual cycle length, regular cycles can vary. Understanding what counts as normal helps you use this period calculator and interpret your own cycle.
  • Cycle Length Range:
    A normal menstrual cycle is typically 21–35 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 28–30 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 2–7 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

The menstrual cycle begins at menarche (first period) and ends at menopause. This context helps you understand when the period calculator applies.
  • 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 menopause, see 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

The menstrual cycle begins on the first day of bleeding and ends just before the next period. Each phase has a clinical meaning.
  • Menstrual Phase (Day 1–~5):
    Cycle day 1 is the first day of bleeding. The uterus sheds its lining. This phase typically lasts 2–7 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.

Period Calculator FAQ

How do I calculate my cycle length?

Cycle length is the number of days from the first day of one period (first day of bleeding) to the first day of the next period. Count day 1 as the first day you see red flow. Example: period started Jan 1, next period started Jan 29 → cycle length 28 days. Track 3–6 cycles and average them for a reliable number. This period calculator uses your average cycle length to project your next period and fertile window.

When is my next period due?

Your next period is estimated as: first day of last period + your average cycle length. Example: last period started March 1, average cycle 28 days → next period due around March 29. Use this period calculator: enter the first day of your last period and your average cycle length (and optionally longest/shortest if your cycle varies) to see when your next period is due and a 6-month forecast.

Is a 35-day cycle normal?

Yes. A 35-day cycle is within the normal range. Average menstrual cycle length is often cited as 28 days, but regular cycles can vary from about 21 to 35 days (and sometimes up to 45). A cycle is generally considered regular if the variation between your shortest and longest cycles in the last 6 months is less than 8 days. If your cycles are consistently 35 days, use 35 as your average cycle length in the calculator.

Can my period stop during pregnancy?

Yes. Periods stop during pregnancy. Once you conceive, the uterine lining is maintained to support the pregnancy, so you do not get a menstrual period. Periods typically do not resume during early breastfeeding (lactational amenorrhea). If you think you might be pregnant or are nursing, this period calculator's forecast may not apply, use a pregnancy test or consult a healthcare provider.

What is the average menstrual cycle length for a 25 year old?

Average menstrual cycle length for people in their twenties is often around 28–30 days, but normal range is about 21–35 days. Age 25 is typically a time of regular cycles. If your cycles are consistently longer (e.g. 32–35 days) or shorter (e.g. 24–26 days), that can still be normal for you. Use your own average in this period calculator for the best prediction.

What is a period and ovulation tracker?

A period and ovulation tracker helps you log your period start dates and cycle length, then projects your next period and fertile window (ovulation ~14 days before the next period). This period calculator is a tracker: you enter first day of last period, period duration, and average cycle length; it shows next period date, probable ovulation, fertile window, and a 6-month forecast calendar.

What are symptoms of a regular period?

Common symptoms of a regular period include: bleeding for 2–7 days, cramping (mild to moderate), bloating, breast tenderness, mood changes, and sometimes headaches or fatigue. Not everyone has the same symptoms. Tracking your symptoms over time (e.g. in a journal or app) can help you recognize your own pattern.

What is a normal cycle?

A normal menstrual cycle is typically 21–35 days from the first day of one period to the first day of the next. The average is often cited as 28 days. Cycles are considered regular if the variation between your shortest and longest cycle (over the last 6 months) is less than 8 days. Bleeding usually lasts 2–7 days. If your cycles are very irregular, very short, or very long, or you have heavy bleeding or pain, see a healthcare provider.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]
ACOG FAQ: Menstruation in Girls and Adolescents

ACOG guidance on normal menstrual cycle parameters, cycle length ranges, and when irregular periods warrant clinical evaluation.

[2]
Reed BG, Carr BR. The Normal Menstrual Cycle and the Control of Ovulation (Endotext)

Comprehensive clinical reference on the hypothalamic–pituitary–ovarian axis, follicular and luteal phase physiology, and cycle variability.

Fitness Reference Note

Informational Use: These calculations (BMI, Calories, etc.) are based on standard statistical formulas and are intended for general reference and goal-setting purposes only.

Consult Experts: This tool does not provide medical advice, diagnosis, or treatment. Results may not be accurate for athletes, pregnant individuals, or those with underlying health conditions.

Health Safety: Always consult with a healthcare professional or qualified trainer before beginning any new diet or intensive exercise program.

Privacy First: All calculations are performed locally in your browser. No health data is stored or transmitted to any server.

© 2026 CalcRegistry Reference Last Logic Update: May 2026Free Online Utility Tools