Wouldn’t it be great to look into the future and see when your next period is coming up?

We made a period calculator that learns about you and your cycles. We use a sophisticated machine learning algorithm to predict your period over the course of the next few months.

- Click on any day to mark it as the beginning of a cycle. This day will be colored red and marked with a star.
- Adjust the length of your period by clicking on one of the days after the beginning of a cycle.
- The period calculator will then
**predict**your next cycles based on your previous cycles. If you show future months, days will have different colors to show the likelihood that you’ll have your period on one of these days. - Note that the further you go into the future, the more fuzzy the prediction gets.
**This is normal. Read on to learn more.** - The likelihood is represented by four colors:

white = almost impossible

low

likely

highly likely - Your cycles will be saved in your browser. If you close this page and come back later, all of your data will be there. However, make sure to use the
**exakt same browser**again.

Let me make a bold statement: All period calculators out there are complete garbage. Why? Because they usually ask you for your **average cycle length** and do a very basic calculation by adding the average length over and over again.

Have you noticed that your natural cycle isn’t always exactly 28 days long? It’s a myth that the female cycle is always 28 days long.

From a medical perspective, if your cycles’ length is between 23 and 35 days, your cycles are considered **regular**.

There was a study in which gynecologists analyzed 9,846 cycles of healthy women between 19 and 45. They found out that only **13% of these women have a typical 28 day cycle**. About 50% of the women had cycles that were longer than 28 days and every tenth cycle was shorter than **25** days.

See the following diagram which shows the distribution of 9846 cycle lengths:

You might say that a regular cycle has about 27 days, give or take a day or two. But that wouldn’t be correct either. The following diagram shows that the cycle lengths can fluctuate quite a bit:

There’s one remarkable take-away: **58% of these women have cycle lengths that vary 7 days or more.**

This means that it’s pretty normal if you experience a cycle that is only 25 days long, followed by another cycle that is 31 days long.

Say you want to calculate your period 3 months into the future. Your cycle lengths change merely by 2-3 days. In the worst case, a normal period calculator would be off by 6-9 days, which is a lot.

**Whenever a period calculator tells you an exact result, it is lying to you.**

We made a better period calculator, which predicts your next periods based on your individual previous cycles and your individual period duration. These individual factors are combined with a general **statistical model** we derived from over 80,000 female cycles.

In other words: Our period calculator gets to know you. It learns more about you and your cycle as you enter more data.

You’ll see that our period calculator is simply honest. Your next menstrual cycle cannot be predicted accurately. Our period calculator takes that into account. If you check 6 months into the future, you’ll notice that the prediction is pretty inaccurate, **because it’s true**. This is the only prediction anyone can ever make about your cycles (if you don’t suppress your cycle with hormones like the pill).

The advantage of our period calculator is that there are still a few days marked *white*. It is highly unlikely that you’ll get your period on one of these days in the future. This allows you to plan ahead, if you have a bit of flexibility in your schedules:

- Planning a long flight and don’t want to have your period on that flight?
- Do you have your next visit to the gynecologist coming up? Plan ahead and schedule an appointment when you don’t have your period.
- Tests, exams, job interviews or anything else coming up and you want to be prepared? Check our period calculator.

admin /AT/ period-calculator /DOT/ com

Notes:

- Medical background data from the German book
*Natürliche Familienplanung Heute*, Springer Verlag, 4. Auflage - This book is based on many studies. One significant study that analyzed female cycles over several years in regards to contraception is this one: http://humrep.oxfordjournals.org/content/22/5/1310.short
- Period Calculator cannot be used as a contraceptive method to avoid pregnancy