Period Calculator

Keeps track of the next 12 menstrual cycles, including period start and end, as well as fertile days.

The first day of your last menstrual period:
Menstrual cycle length:
Period length:

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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

This period calculator determines the most important data of the menstrual cycle in a personalised manner, based on the first day of the last cycle, average cycle length and period duration in days.

The use of this calculator facilitates planning around the menstrual cycle period starts and fertile windows and can be used for estimations by women with fairly regular cycles.

The menstrual cycle occurs in fertile females every 28 days, in average. The length may vary between 26 and even 36 days. Each cycle consists of three different phases, controlled by the endocrine system: follicular phase, ovulation and luteal phase. Depending on egg and sperm viability, the fertile window is estimated at between 5 day before ovulation and 2 days after.

The bleeding period of the menstrual cycle is usually called period and has a length varying from 2-9 days and different blood debits in each woman.


Wilcox AJ, Baird DD, Weinberg CR (1999) Time of implantation of the Conceptus and loss of pregnancy. New England Journal of Medicine 340 (23): 1796–1799

Beckmann CRB. (2010) Obstetrics and Gynecology. Lippincott Williams & Wilkins. pp. 306–307

Specialty: Obstetrics Gynecology

System: Reproductive