Creation calendar is calculated according to creation week. Let’s read the first chapter of Genesis.
Genesis 1: 14-19  And Elohim said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:  And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.  And Elohim made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.  And Elohim set them in the firmament of the heaven to give light upon the earth,  And to rule over the day and over the night, and to divide the light from the darkness: and Elohim saw that it was good.  And the evening and the morning were the fourth day.”
Notice it says the EVENING and MORNING were the fourth day. Why did it not say morning and evening? When the earth was created darkness was on the face of the deep.
Gen 1:2 –  And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of Elohim moved upon the face of the waters.  And Elohim said, Let there be light: and there was light.  And Elohim saw the light, that it was good: and Elohim divided the light from the darkness.  And Elohim called the light Day, and the darkness he called Night. And the evening and the morning were the first day. On the first day he called the evening as the beginning of the day.
When we get to the 4th day of the creation, there is still darkness. It says he created light, but have you heard of “earth light”? When the astronauts were in space they saw the “earth light’ confirming what the Scriptures say.
But when the time came for creating the 2 great lights in the heavens, the Scriptures say the moon was created first and the sun next. The moon cannot have any light without the sun. This is why the Scriptures record that the evening was the beginning of the day. We start the day at sundown. We celebrate the Sabbath from sundown Friday to sundown Saturday. Every day begins and ends at the sundown. When the Passover is kept the Scriptures say on the 14th day at even. And then goes on to say that the 15th day of the first month (Abib) is the day of Passover. When you follow the Scriptures correctly then you keep the correct day.
Evening, sunset marks the end of one day and the beginning of the next, with Morning marking the beginning of the light part of the day; when the earth has finished its complete revolution on its axis it comes back to where it started its rotation, marking the end of a 24 hour cycle or period called day, and every day since that time has been marked out by the revolution of the earth on its axis. According to this tim could never be lost nor changed, for it is controlled by the astronomical law set in motion at creation.
We want to show which time to keep the new moon. Is it a dark moon or a sliver? Again we turn to Gen 1: 14-19.  And the evening and the morning were the fourth day.” Now again we see a dark moon because the sun has not been created yet. We have a new moon, a dark moon. Twelve hours later the sun is created and this starts the light for the moon. So which was created first? If the Scriptures are correct then we have to know the new moon is a dark moon.
Notice on Yahweh’s Creation Calendar you will see 3 dates for each day.
The top one is the Solar day, then the Lunar day, and the bottom is the Gregorian day.
The Solar New Year is always starts on March 17, and each new Solar month begins on the 17th of each Gregorian month. Solar months are 30 and 31 days, Lunar months are 29 and 30, and the Gregorian days are 30 and 31 with the exception of February. Yahweh is perfect in all his ways.
He says he set his calendar in the sky where man cannot alter it.
Jeremiah 33:20 Thus saith the YAHWEH; If ye can break my covenant of the day, and my covenant of the night, and that there should not be day and night in their season;  Then may also my covenant be broken with David my servant, that he should not have a son to reign upon his throne; and with the Levites the priests, my ministers.  Thus saith the YAHWEH; If my covenant be not with day and night, and if I have not appointed the ordinances of heaven and earth;  Then will I cast away the seed of Jacob, and David my servant, so that I will not take any of his seed to be rulers over the seed of Abraham, Isaac, and Jacob: for I will cause their captivity to return, and have mercy on them.”
Jeremiah 31:  Thus saith the YAHWEH, which giveth the sun for a light by day, and the ordinances of the moon and of the stars for a light by night, which divideth the sea when the waves thereof roar; The YAHWEH of hosts is his name:
 If those ordinances depart from before me, saith the YAHWEH, then the seed of Israel also shall cease from being a nation before me for ever.
 Thus saith the YAHWEH; If heaven above can be measured, and the foundations of the earth searched out beneath, I will also cast off all the seed of Israel for all that they have done, saith the YAHWEH.
Astronomical law proves Creation Calendar every year and therefore Creation Calendar is a solar, lunar, Biblical calendar. There is not another calendar like this to put mankind back on true time as it was in the beginning. The Catholic church is the one who changed the times for the beginning of the months and years. The Gregorian calendar is 75 days off every year for the New Year.
Yahweh starts his New Year in the Spring when every thing is new and fresh with new growth. The wintertime is the end of the lunar year time of the seasons.
The lunar months are set according the first new moon that falls closest to the vernal equinox. The new moon can be before the vernal equinox or after it and this sets the time of the Passover or Yahshua’s Supper.
The Lunar months always begins with the New Moon. You cannot have the Passover fall before the 17th of the March or you will be keeping it twice in the year. This is a solid rule that cannot be disputed. If you keep the New Moon closest to the vernal equinox then Passover is 14 days later at sundown.
Leviticus 23:  These are the feasts of the YAHWEH, even holy convocations, which ye shall proclaim in their seasons.
 In the fourteenth day of the first month at even is the YAHWEH’s Passover.
 And on the fifteenth day of the same month is the feast of unleavened bread unto the YAHWEH: seven days ye must eat unleavened bread.
 In the first day ye shall have an holy convocation: ye shall do no servile work therein.”
The Scriptures say the Passover begins at even, which begins the 15th day of the month. Even means the end of the 14th day beginning the 15th day.
Daniel makes plain that there is a time the beast will think to change times and laws. This we have seen happen in the change of the times of the New Year, the beginning of the months, and even to doing away with the feast days which are the heart of the law of the sanctuary system, and setting up in their place the pagan holidays. Without the Feast days we would have no salvation.
How can this be so? Let’s lay it out as the Scriptures teach it.
At the Passover time, Yahshua was crucified on the sixth day, rested in the grave over the Sabbath, and resurrected on the first day of the week, took a wave sheaf to heaven and offered it before the Father. It was accepted and a new and living way was set up for the Sanctuary system of true worship.
Hebrews 10:  Now where remission of these is, there is no more offering for sin.
 Having therefore, brethren, boldness to enter into the holiest by the blood of Yahshua,  By a new and living way, which he hath consecrated for us, through the veil, that is to say, his flesh.
The beginning of the year and months have changed several times since the time of the Crucifixion.
But Yahweh set his time in the sky in the beginning and it has never been lost. He says I change not. Malachi 3:6  For I am the YAHWEH, I change not;
The rotation of the earth was set for keeping the perfect time and as the earth rotates around the sun and the moon moves around the earth, Yahweh set it all in perfect motion and it is still on that rotation today.
Numbers 23:  Elohim is not a man that he should lie; neither the Son of man that he should repent: hath he said, and shall he not do it? Or hath he spoken, and shall he not make it good?