Day Periods
The first 2 levels of dividing the year (from your birthday to your birthday) are the 52-day and the 28-day.
52 x 7 (with a day left over- Joker)
uses the Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune cards from your chart
28 x 13 (with a day left over- Joker)
uses every card beginning with the Sun/Birth all the way out through the Earth card
The card lasts for that entire period of days. So, you get 52 days under your Mercury card, the next 52 under your Venus card, etc.
At the same time, you are running the 28 days: the first 28 are your Sun/birth card. The next 28 are under the Mercury card, etc.
I found an online calculator! It will be a bit tedious going bit by bit, but it is an option for those with no books or PDF documents.
http://www.timeanddate.com/date/dateadd.html
Note: Feb 29 (Leap Day) is not a feature in these day-periods unless you happen to be born on it.
Using a calendar year that has a Leap Day will throw off the dates for the months following.
These are small screenshots from Iain McLaren-Owens'
SS 8 Magian Card Tables to show the divisions.