How do I predict my next period?

Add your average cycle length to the first day of your last period. For example, if your last period started April 1 and your cycle is 28 days, your next period is expected April 29. Our calculator does this automatically and predicts multiple future cycles.

What is a normal menstrual cycle length?

A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the average. Cycles shorter than 21 days or longer than 35 days may indicate a hormonal imbalance and are worth discussing with a healthcare provider.

Can I use this calculator for irregular cycles?

Yes. For irregular cycles, calculate your average cycle length by adding up 3–6 recent cycles and dividing by the number of cycles. Use that average as your input. For very irregular periods, consider tracking with basal body temperature or ovulation tests.

What are the phases of the menstrual cycle?

The cycle has four phases: (1) Menstrual phase — your period (days 1–5), (2) Follicular phase — follicles develop, estrogen rises (days 6–13), (3) Ovulation — egg is released (around day 14), (4) Luteal phase — progesterone rises, body prepares for pregnancy (days 15–28).

How do I calculate my fertile window from my period?

Ovulation typically occurs 14 days before your next period. Your fertile window spans 5 days before ovulation through ovulation day. To find it: subtract 14 from your cycle length to get ovulation day, then count 5 days back for fertile window start.

How many days after my period do I ovulate?

For a 28-day cycle, ovulation is typically around day 14 — about 14 days after your period starts. For a 30-day cycle, it would be around day 16. The rule of thumb: ovulation day = cycle length minus 14.

Why is my period calculator different from last month?

Cycle length naturally varies due to stress, illness, weight changes, travel, or hormonal fluctuations. A variation of 1–7 days is normal. If your cycles vary by more than 7 days regularly, consider consulting a healthcare provider.

How accurate is a menstrual cycle calculator?

Period calculators are most accurate for women with regular cycles. They provide estimates based on your average cycle length. For irregular cycles, the prediction may be off by several days. Tracking multiple cycles improves accuracy over time.

What is the luteal phase and why does it matter?

The luteal phase is the second half of your cycle, from ovulation until your next period (typically 14 days). It's when progesterone rises to prepare the uterus for pregnancy. A short luteal phase (under 10 days) can make conception difficult.

Can this calculator help with pregnancy planning?

Yes! The calculator predicts your fertile window and ovulation date, which are critical for pregnancy planning. The highest chance of conception is during the 2–3 days before ovulation and on ovulation day itself.

Menstrual Cycle Calculator

Our free menstrual cycle calculator helps you predict your next period, understand each phase of your cycle, and identify your fertile window. Simply enter the first day of your last period and your average cycle length to get accurate predictions for multiple upcoming cycles — including period dates, ovulation windows, and phase breakdowns.

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calendar_today Updated: April 2026

auto_awesome AI Insights AI

New

First Day of Last Period

Cycle Length 28 days

21 days (short) 28 days (avg) 35 days (long)

Period Duration 5 days

2 days 7 days

Current Status Follicular

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Cycle Day

—

Days to Period

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Days to Ov.

This Month

Period Fertile Ovulation Today

calendar_month Next Period

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calculating...

egg Ovulation & Fertile Window

Ovulation Date —

Fertile Window —

Peak Fertility —

Cycle Phases

Period

Luteal

Day 1 Follicular Ov. Day 28

Upcoming Cycles

Input Values

First Day of Last Period

Average Cycle Length

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auto_awesome AI Analysis

Cycle Summary (28-day cycle, LMP Apr 1):

Next period: April 29, 2026
Ovulation: ~April 15, 2026
Fertile window: April 10–15
Current phase: Follicular Phase

Cycle predictions are estimates. Track 3+ cycles for best accuracy. Consult a healthcare provider for irregular periods.

lightbulb Tips

•Normal cycle: 21–35 days, avg 28
•Track first day of flow, not spotting
•Ovulation = cycle length minus 14 days
•Track 3+ cycles for reliable average

cycle Cycle Phases (28-day)

Menstrual Days 1–5

Follicular Days 6–13

Ovulation Day 14

Luteal Days 15–28

Cycle Length Norms

Short cycle 21–24 days

Average cycle 25–30 days

Long cycle 31–35 days

Period Duration

Normal range 2–7 days

How to Use This Calculator

calendar_month

Enter Last Period Date

Select the first day of your most recent menstrual period (not spotting).

cycle

Set Cycle Length

Enter your average cycle length (21–35 days). The average is 28 days.

analytics

View Predictions

See your next period date, ovulation window, and cycle phase breakdown.

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Plan Multiple Cycles

Get predictions for up to 12 upcoming cycles for long-term planning.

The Formula

A menstrual cycle begins on the first day of your period and ends the day before your next period. The average cycle is 28 days but can range from 21 to 35 days. Ovulation typically occurs 14 days before the next period (luteal phase = 14 days).

Next Period = LMP + Cycle Length

lightbulb Variables Explained

Next Period Predicted start date of next menstrual period
LMP First day of last menstrual period
Cycle Length Average number of days between periods (21–35 days)

tips_and_updates Pro Tips

Track your period on the first day of flow, not spotting

A normal cycle ranges from 21 to 35 days

Period length of 2–7 days is considered normal

Stress, illness, and lifestyle changes can shift your cycle

Track 3+ cycles to determine your true average length

Period apps and basal body temperature improve accuracy for irregular cycles

Menstrual Cycle Calculator - Predict Your Next Period

Our free menstrual cycle calculator predicts your next period date, tracks your cycle phases, and identifies your fertile window. Enter your last period date and average cycle length to get accurate predictions for multiple upcoming cycles.

Period Prediction Calculator

Predict your next period by entering the first day of your last period and your average cycle length. Our calculator adds your cycle length to your last period date to predict when your next period will arrive — and continues predicting for up to 12 cycles ahead.

Menstrual Cycle Length Calculator

Track your menstrual cycle length by recording the first day of consecutive periods. Most cycles range from 21 to 35 days. A 28-day cycle is average, but 'normal' is whatever is consistent for you. Cycles that vary by more than 7 days may indicate hormonal changes worth monitoring.

Fertile Window & Ovulation Calculator

Your menstrual cycle calculator also predicts your ovulation date and fertile window. Ovulation typically occurs 14 days before your next period. The fertile window spans 5 days before ovulation through ovulation day — a total of 6 days when pregnancy is possible.

Period Calculator for Irregular Cycles

If your periods are irregular, calculate your average cycle length using 3–6 recent cycles. Add up the days and divide by the number of cycles. Enter this average for the most accurate predictions. For highly irregular periods, consider tracking basal body temperature alongside this calculator.

Understanding Your Menstrual Cycle Phases

Your menstrual cycle has four phases: Menstrual (days 1–5), Follicular (days 6–13), Ovulation (around day 14), and Luteal (days 15–28 for a 28-day cycle). Understanding each phase helps you predict symptoms, energy levels, and fertility throughout the month.

Frequently Asked Questions

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