Since the new moon can occur at any time throughout a day, it makes sense to me to call the first day that everyone around the world can be under a new moon, the first day of the month. For our calculation purposes, a calendar day starts when the “average day” sun sets at the International Dateline. A month starts the first day that there was a New Moon in the previous 24 hours at the “average day” sunset of 6:00pm at the International Date Line.
Start of the year
The same logic is used for the first day of the year. The year starts with the first day of the first month after the Spring equinox. Taking our six hour adjustment into account (sunset not midnight) the day after the day of the Northern Hemisphere Spring equinox is the start of Spring, and the earliest that the first month of the year should start. Under these rules, each new year will always start somewhere within the first 30 days of Spring. Since we look at what the situation is at the start (6:00pm at IDL) of a day, in the rare case of where the equinox and the new moon conjunction both occur in the previous (sunset to sunset) 24 hour period, then the next day is both the new month and new year. Which is the case in 2015.
Before we can pencil in the Holy Days, we need a basic calendar. This can be a normal calendar with enough room to write on, or we can start with just a list of all the important dates, and transfer them over later. The place to start is to first find the March equinox and the times of the New Moons for the year. Make sure that any times given are in Universal Time (abbreviated as “UT” or “UTC”). There is less than one second difference between UT and UTC, so for our purposes either can be used. These dates and times can be found from published charts and from the Internet (e.g. U.N. Naval Observatory [http://aa.usno.navy.mil/data/docs/MoonPhase.php], Geoscience Australia, Nasa, http://www.calendar-12.com/moon_phases [scan down to find UTC times in the RH column]). The times for the New Moons on wall calendars are usually local times, so corrections have to be made to bring them back to UT, and that can make the calculations more complicated.
This is how I do it, but there may be other ways of doing the calculations.
Go into http://www.calendar-12.com/moon_phases
It will usually come up with the current year. To get next years phases, scroll down past the first block of dates and you will see where you can move the year forward or backward. Set the year you want, and let it recalculate.
Again scroll down to the second block of dates and times and UTC is on the RH side of the block.
Key in the first day of the year. Number of phases - try 50. Format - display by phases. Then click on "get data".
Now you have all the information you need.
Take the date of the two equinoxes and write them on the calendar. Just for interest, I pencil in the longest and shortest days as well.
Look at the date and time for each of the new moons. If the time is less than 6:00 hours UTC, take the date given and mark it on the calendar. If the time of day is 6:00 hours UTC or greater, increase the date by one, and mark it on the calendar. This is the start of each month.
When all the new moons are done, look for the closest new moon after the March equinox (can't be the same day). That is the first day of the new year for God's calendar.
Count down 14 days, and mark the evening before as the Last Supper. The 14th is the day the Passover lambs (and Christ) were killed. The 15th day is the first Holy Day of Unleavened Bread. Seven days later (21st) is the Second Holy Day of Unleavened Bread.
From the Sunday (the day after the Sabbath) during Unleavened Bread, count 50 days (seven full weeks plus one day), and that Sunday is Pentecost.
The first day of the seventh month is Trumpets, followed by Atonement on the 10th day, and Tabernacles starting on the 15th day, and Last Great Day on the 22nd day.
While this information is made freely available (Mat 10:8b) , and can be printed out, it is done with the understanding that there will only be fair and honest use of the material, and that it will be copied in full with no alterations.