Contraception

Your cycle doesn’t show you all your fertile days

According to the moon phase method, a second fertile window opens every month: around the moon position of your birth. Your calendar overlays both rhythms, as a simple traffic light of green and red days. Calculated from your actual period start, to the exact day and in your time zone.

Calculate my month The days your cycle misses

No account · Calculated for you · One month for €9

Two rhythms

Knowing your fertile days: most people only look at the cycle

If you want to understand your body or plan naturally, you know the usual ways of finding the fertile days. Each has its value, and all of them follow the same beat: your monthly cycle.

  • Calendar methodCounts the days from your last bleeding and estimates the fertile time. Quick to do, but easily off when your cycle varies.
  • Basal temperatureShows ovulation through a small temperature rise, but only after it has happened. It offers little for looking ahead.
  • Cervical mucusAnnounces the fertile days in advance when the mucus turns clear and stretchy. Requires daily observation and some practice.
  • Cycle appsConvenient on your phone, but most of them simply project the calendar forward and estimate instead of truly reading your body.

All of these look at the same thing: your monthly cycle.

According to the moon phase method, a second rhythm has a say as well.

The physician Dr. Eugen Jonas originally developed his method in the 1950s for exactly this purpose: natural birth control. Evaluating thousands of women, he found a surprising ratio:

85%
of conception readiness depends, according to Dr. Jonas, on your very personal moon rhythm, and only 15 percent on the familiar monthly cycle.

That is why your calendar overlays both rhythms: the cautious estimate from your cycle and your personal moon window.

How your calendar is made

Three layers, one calm view of your month

Your calendar is built from three things: your actual period start, your usual cycle length and the moon you were born under.

01

Your period anchors the month

Your cycle begins with the first day of bleeding. Ovulation usually follows around 14 days before the next period. Because sperm can survive for several days, the fertile time starts earlier. These are exactly the days your calendar marks.

02

Your moon window joins in

At the moment you were born, the sun and the moon stood at an angle that belongs only to you. Whenever this angle returns, roughly every 29 days, the moon phase method sees an additional fertile window of about three days.

03

The traffic light brings it together

Every day of your month gets a colour: green for days without fertile signs, red for fertile days, and dark red when cycle and moon point to the same day. The following month is clearly marked as an estimate.

This is how your month reads at a glance: green are the calm days, red the fertile ones, dark red the days when both rhythms coincide.

Your calculation

Calculate your current month

Enter the first day of your current period and see immediately what your month looks like: how many days your cycle marks and when your moon window falls. Available to adults aged 18 and over; your details are only used for the preview and the purchase flow.

First day of my current period *

No more than 45 days ago and not in the future.

My usual cycle length

If you are unsure, use 29 days as a cautious starting estimate.

My date of birth *

From this I calculate your personal moon window.

My time of birth

Even the approximate time of day makes your calendar more precise. Without it, I calculate with 12:00.

My place of birth

Sets the time zone of your birth. Daylight saving is handled automatically.

My current location

I show your calendar in the local time of your current location.

My name (optional)

Your look-back at last month: free

How it works

From your period start to your monthly calendar

1

Enter the current date

The actual first day of bleeding is the basis of your month. The calendar works with your real cycle, not with an average.

2

Receive the calendar for €9

You receive your complete monthly calendar as a lovingly designed PDF by email, with a clearly marked outlook for the following month.

3

Recalculate with your next period

Your cycle is alive and can shift. As soon as your next period actually starts, a fresh calendar is created with the new date.

Your month as a PDF
My monthly calendar
with a traffic light for every day

Your everyday companion

One month, matched to your current period

Your purchase includes the personal calendar for your current cycle month. The second month is a non-binding estimate for orientation.

  • A simple traffic light for every day of your month
  • Period, ovulation and fertile days named in plain words
  • Your personal moon window, calculated from your birth
  • The following month as a clearly marked estimate
  • Calculated in your local time, with automatic daylight saving
  • A PDF to save and print, right after payment
€9one-off for each current cycle
Enter details now

View the sample PDF: this is what your monthly calendar looks like

The story behind it

From old knowledge to birth control by the moon

People have watched the moon since time immemorial. It accompanies the nights, moves the tides and has stood for change, rhythm and return since ancient times. Many traditional cultures observed it closely: for sowing and harvest, for sleep and birth, and also for the female cycle.

The physician Dr. Eugen Jonas took up these old observations again in 1956, first not for conception, but for natural birth control. Evaluating thousands of women, he became convinced that the moon phase of a woman's birth holds a second fertility rhythm.

I have made this method calculable again with modern astronomy: verifiable, precise to the day and individual for every woman.

Good to know

Frequently asked questions

What do the green and red days mean?

Red days are the days on which the calculation shows fertile signs, from your cycle, your moon window or both. Green days are the days on which it finds nothing fertile. They are considered likely infertile and are often called “safe days”, but they are never completely certain.

How are my fertile days calculated?

Your period start and cycle length are used to estimate ovulation, usually around 14 days before the next period. Because sperm can survive for several days, the calendar also marks the days before it. On top of that comes your personal moon window from the angle of sun and moon at your birth.

What is the moon window?

According to the moon phase method, the angle between sun and moon from the moment of your birth returns in every lunar cycle, roughly every 29 days. Around this moment an additional fertile window of about three days applies. I calculate it astronomically from precise ephemeris data.

My cycle is irregular. Does this still work?

The more irregular your cycle, the less certain any estimate becomes. That is exactly why your calendar is anchored to your actual period start and freshly calculated with every new period. If your cycle varies a lot, please treat the green days with extra caution.

Is this calendar a reliable method of contraception?

No. It is a personal companion that shows you your rhythm. For contraception, please continue to rely on a method you trust, and discuss medical questions with your doctor.

Why does the purchase cover one month only?

Your calendar is anchored to your actual period start. Because the next start can shift, the next month needs the current date again. That keeps the calculation honest.

What do I receive for €9?

Your personal monthly calendar as a lovingly designed PDF for the current cycle, with the traffic light for every day and a clearly separated, estimated outlook for the following month. One-off payment, no subscription.

What happens to my details?

Your entries are only used for the preview in your browser and for the purchase flow. You need no account and no registration.

Who is behind this
Portrait of German Besler in front of the Bavarian Alps

German Besler

Spiritual healer · Hinterstein in the Bavarian Alps, Germany

German lives and works in Hinterstein, a mountain village in the Bavarian Alps in Germany. His work is energetic, not medical: attention for what lies beneath the visible, calm and firmly grounded.

The idea of the birth moon never let him go. He has made the method calculable again with today's astronomical data, so that you know your own rhythm and can plan your month in peace.

More about German and his work at germanbesler.de

Your first step

Know your month before it starts

In one minute you see your last month in the traffic light for free, and can take your current month with you as a PDF.

Calculate my month

No account · Calculated for you · One month for €9