What is a menstrual cycle?

A menstrual cycle is the time from the first day of one period to the first day of the next period. The average cycle length is 28 days, but it can normally range from 21 to 35 days.

How accurate is this period calculator?

This calculator provides a good estimate, especially if your periods are regular. However, factors like stress, diet, exercise, and illness can cause your period to arrive earlier or later than predicted. It's a tool for planning, not a medical diagnosis.

What if my periods are irregular?

If your cycle length varies a lot, this calculator will be less accurate. It's best to track your periods for several months and use the average cycle length for the calculation. If your periods are very irregular, it's a good idea to speak with a healthcare provider.

Period Calculator

MEDICAL DISCLAIMER: This calculator provides an estimate for informational purposes only and is not a substitute for professional medical advice. For any health concerns, please consult a qualified healthcare provider.

Your Next Period Is Estimated To Start On:

Future Period Predictions

Period Cycle	Estimated Start Date

How is the Next Period Calculated?

Predicting your next period is based on understanding your menstrual cycle. A cycle is counted from the first day of one period to the first day of the next.

The Calculation: The calculator takes the date you provide as the start of your last period and adds your average cycle length to it. For example, if your last period started on January 1st and your average cycle is 28 days, your next period is predicted to start on January 29th.
Cycle Length: While 28 days is often cited as the average, a "normal" cycle can range anywhere from 21 to 35 days. Using your own average cycle length makes the prediction more accurate for you.
It's an Estimate: This tool provides an educated guess. It's important to remember that factors like stress, changes in diet or exercise, travel, and illness can all affect the timing of your period.

The Surprising History: From Superstition to Science

For most of human history, the menstrual cycle was poorly understood and often surrounded by myth and superstition. Tracking was rudimentary, relying on simple calendars or lunar cycles. There was little to no scientific understanding of the hormonal processes driving it all.

The true scientific revolution in understanding periods occurred in the 20th century. Researchers began to identify the key hormones—estrogen and progesterone—and mapped out their rise and fall throughout the cycle. This discovery transformed the view of menstruation from a mysterious event into a predictable, biological process. It paved the way for everything from modern fertility treatments to the development of hormonal birth control, and eventually, the simple but powerful period tracking calculators we use today.

Explore More Health & Fitness Tools

Ovulation Calculator: Find your most fertile days within your cycle.
Pregnancy Due Date Calculator: A helpful tool if you're trying to conceive.
BMI Calculator: Monitor your overall health status.
Daily Calorie Calculator: Understand how nutrition impacts your cycle and well-being.
Water Intake Calculator: Staying hydrated can help with PMS symptoms.
Ideal Weight Calculator: Understand healthy weight ranges.
Body Fat Calculator: Learn more about body composition.
TDEE Calculator: See how your energy needs change.
BMR Calculator: Know your baseline metabolism.
Heart Disease Risk Calculator: A tool for long-term health awareness.

Frequently Asked Questions (FAQ)

What is a normal menstrual cycle length?

While 28 days is the most commonly cited average, a normal cycle for an adult can range from 21 to 35 days. For teenagers, cycles can be longer and more irregular. "Normal" is what is consistent for you.

My periods are irregular. Can I still use this calculator?

You can, but the prediction will be less reliable. For the best result, track your cycle lengths for 3-4 months and use the average length in the calculator. If your cycles are consistently very irregular, it's a good idea to discuss it with your doctor.

What can cause my period to be late?

Many factors can delay a period besides pregnancy. Common causes include high levels of stress, significant changes in diet or exercise, travel, illness, and certain medications. If your period is significantly late and you have concerns, you should consult a healthcare provider.