Praktické

Kalkulačka menštruačného cyklu

Menstrual Cycle Calculator

First Day of Last Period

Cycle Length (days)

Period Length (days)

What is Period Calculator?

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A period (menstrual cycle) calculator predicts future menstruation dates based on cycle length and period duration. The average cycle is 28 days, but cycles from 21 to 35 days are normal. Tracking helps identify irregularities and plan around key life events.

Calkulon makes complex calculations simple — built for students and everyday problem-solvers.

How to Period Calculator

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1Record the first day of your last period (day 1)
2Add cycle length to find the next period start date
3Add period length to find the end date
4Repeat for subsequent cycles

Worked Examples

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Example 1

Given:Last period: 1 March · 28-day cycle

Výsledok:Next period: 29 March · Fertile window: ~15–19 March

Menstrual Cycle Phases

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Phase	Days (28-day cycle)	Key Events
Menstruation	1–5	Uterine lining sheds
Follicular	1–13	Follicles develop in ovaries
Ovulation	~14	Egg released — peak fertility
Luteal	15–28	Progesterone rises; PMS may occur

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Pro Tip

Cycle irregularity of a few days is normal. Consult a doctor if cycles are consistently shorter than 21 days, longer than 35 days, or if you experience very heavy bleeding.

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Did you know?

The word "menstruation" comes from Latin "mensis" (month) and Greek "mene" (moon). Many ancient calendars were based on the lunar cycle (~29.5 days), close to the average menstrual cycle.

References

›Menstrual cycle — Wikipedia

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Deep Dive

Read the full guide on how to use this calculator effectively

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Formula-verified for precision

Reviewed October 2026

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