Moontime Diary 2023

Dr Eugen Jonas’ Lunar Fertility Calculator

Every woman must know about Dr Eugen Jonas’ Lunar Method and Fertility Calculator!

I have always been aware of and interested in my hormonal cycle. However, when I learned the practical way women have another fertility cycle running parallel, I was more than surprised. In other words, we can be fertile twice a month, and it can happen even on ‘impossible days’. How? Please read on and find out…

In the 1950s, when abortion laws were hotly discussed and introduced, first in Russia and then in Hungary, women and the medical community were still left with the dilemma of the physical, mental and emotional repercussions of the law permitting this procedure.

As a young Slovakian doctor in Nitra, Eugen Jonas started to look at this challenge differently. His mission was: ‘How to plan a pregnancy and avoid unwanted ones.’


Traditionally doctors were aware of the moon’s effect on females’ fertility cycle, and Dr Jonas started thinking about the Babylonian saying, “Woman is only fertile during a certain phase of the moon.” His research led him to develop a specific calculation method which he first tested on family and friends. He observed and collected data over several years and found it supported his ideas.

Jiri Malek, a gynecologist in Prague, was the first to show scientific interest in Dr Jonas’s thesis and invited Dr Jonas to the Maternity Clinic in Bratislava. Here Dr Jonas was able to do more research and prove his method at the hospital. Again, his findings confirmed his discoveries.

The medical profession started to show interest, and Dr Jonas was invited to talk worldwide, but then, during the communist government, his work was nearly lost to the west. Dr Jonas continued his research and found many coherencies and connections between the moon and the female fertility cycle.

Dr Jonas’ ‘Lunar Fertility Calculator

He discovered that using the first day of the last period to calculate the delivery date is rarely correct. This calculation is still used by the medical profession today but is based only on the woman’s hormonal cycle.
Dr Jonas calculated the conception date using the position and phase of the moon at birth in the female natal chart. He found that the fertile days are just the three days before the moon is at the same phase as it was at her birth. He used this method to calculate the conception day and, from there, the possible delivery date of the baby.

Dr Jonas also found that the gender of the child is determined by the gender of the (tropical) zodiac sign the moon is in during conception. While male signs like Aries, Leo and, Libra etc., seem to produce more baby boys, female signs like Taurus, Cancer, Scorpio turn out more baby girls.

Dr Jonas developed his ‘Lunar Fertility Calculator’ over many years of research and claimed a 97% accuracy in determining the

  • Fertility Cycle – Useful for both conception and contraception!
  • Gender of a child conceived.

Once you determine which days are best for conceiving (and determining the gender), you must have or avoid intercourse the three days before and after the chosen days for conception.

There are other factors, too; however, awareness of these facts and possibilities empowers any girl and woman. It gives women a choice and chance to create more consciously and can save us much heartache, effort and time.Moontime Diary 2024

Here are some links for further reading and a calculator to find out your particular dates:

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For daily lunar information, check out the Moontime Diary 2024

Many Moon Blessings,


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