Period Calculator 2025

Your Cycle Information

First Day of Last Period

Select the first day your last period started

Average Cycle Length (days)

Average is 28 days. Normal range: 21-35 days.

Period Duration (days)

Average is 4-5 days. Normal range: 2-7 days.

Cycles to Predict

Ovulation

Most fertile days - egg is released from ovary

Day 15 of your 28-day cycle

Your Predictions

Next Period Expected

10 Jan

14 days from now

Fertile Window

22 Dec - 28 DecNOW!

Highest chance of conception during these days

🥚 Expected Ovulation

Saturday, 27 December

Approximately 14 days before next period

PMS Phase Starts

3 Jan

7 days before period - symptoms may appear

Future Period Predictions

Cycle	Period Dates	Fertile Window	Ovulation
1(Past)	13 Dec 2025 to 17 Dec 2025	22 Dec - 28 Dec	27 Dec
2	10 Jan 2026 to 14 Jan 2026	19 Jan - 25 Jan	24 Jan
3	7 Feb 2026 to 11 Feb 2026	16 Feb - 22 Feb	21 Feb
4	7 Mar 2026 to 11 Mar 2026	16 Mar - 22 Mar	21 Mar
5	4 Apr 2026 to 8 Apr 2026	13 Apr - 19 Apr	18 Apr
6	2 May 2026 to 6 May 2026	11 May - 17 May	16 May

🌸 Understanding Your Menstrual Cycle

Menstrual Phase

Days 1-5 (approx)

Period occurs. Uterine lining sheds. You may experience cramps, fatigue, and mood changes.

Follicular Phase

Days 1-13 (approx)

Overlaps with menstruation. Estrogen rises, egg develops. Energy and mood typically improve.

Ovulation

Day 14 (approx)

Egg is released. Peak fertility. You may notice increased libido and clearer skin.

Luteal Phase

Days 15-28 (approx)

Progesterone rises. PMS symptoms may occur. Body prepares for pregnancy or next period.

Important Notes

📌 About These Predictions

• Based on average cycle length you provided
• Assumes regular cycles (predictions vary if irregular)
• Ovulation can vary by a few days
• Not to be used as sole birth control method

⚠️ Consult a Doctor If

• Cycles are shorter than 21 or longer than 35 days
• Period lasts more than 7 days
• Severe pain or heavy bleeding
• Missed periods (if not pregnant)

What is a Period Calculator?

A Period Calculator helps you predict your menstrual cycle by calculating your next period date, ovulation day, and fertile window based on your cycle history. It's useful for:

📅 Planning events and travel around your period
💊 Knowing when to expect PMS symptoms
👶 Identifying your most fertile days
📊 Tracking cycle regularity for health insights

How to Use

1Enter the first day of your last period
2Input your average cycle length (28 days is typical)
3Enter how long your period usually lasts
4View predictions for your next period & fertile window
5Check the calendar for multiple future cycles

Understanding Cycle Length

Short Cycles (21-24 days)

• Ovulation around day 7-10
• Shorter follicular phase
• May indicate hormonal changes

Normal Cycles (25-35 days)

• Ovulation varies by cycle length
• 28 days is the average
• Most common range

Long Cycles (36+ days)

• Ovulation occurs later
• May indicate PCOS
• Consider consulting a doctor

⚠️ Important Health Notes

🚫 Not for Contraception

This calculator should not be used as a birth control method. Ovulation timing can vary significantly, and sperm can survive for up to 5 days. Use reliable contraception methods.

👩‍⚕️ When to See a Doctor

• Cycles shorter than 21 or longer than 35 days
• Severe cramps or heavy bleeding
• Missed periods (if not pregnant)
• Bleeding between periods

Frequently Asked Questions

How accurate is the period calculator?

For women with regular cycles, the calculator is quite accurate. Predictions are based on your average cycle length. However, factors like stress, illness, travel, weight changes, and hormonal fluctuations can cause variations. Track your actual periods to get better averages over time.

What is a normal menstrual cycle length?

A normal cycle length ranges from 21 to 35 days, with 28 days being the average. Cycles shorter than 21 days (polymenorrhea) or longer than 35 days (oligomenorrhea) may indicate hormonal imbalances and should be discussed with a doctor.

When is the fertile window in my cycle?

The fertile window is approximately 6 days: the 5 days before ovulation and the day of ovulation itself. Sperm can survive up to 5 days in the reproductive tract, while an egg survives 12-24 hours. For a 28-day cycle, this is typically days 9-14.

How is ovulation day calculated?

Ovulation typically occurs 14 days before your next period (not 14 days after your last period). This is called the luteal phase, which is relatively consistent at 14 days for most women. So for a 28-day cycle, ovulation is on day 14; for a 32-day cycle, it's on day 18.

Can I use this calculator for birth control?

This calculator should NOT be used as a sole method of birth control. The calendar/rhythm method has a high failure rate (up to 25%) because ovulation timing can vary. Use reliable contraception methods and consult with a healthcare provider for family planning.

What are the phases of the menstrual cycle?

The four phases are: 1) Menstrual (days 1-5) - uterine lining sheds, 2) Follicular (days 1-13) - estrogen rises, egg develops, 3) Ovulation (day 14) - egg is released, peak fertility, 4) Luteal (days 15-28) - progesterone rises, preparing for pregnancy or next period.

Why is my cycle irregular?

Irregular cycles can be caused by stress, significant weight changes, intense exercise, PCOS (polycystic ovary syndrome), thyroid disorders, perimenopause, or other hormonal imbalances. If your cycles are consistently irregular, consult a gynecologist for evaluation.