I keep two kinds of homeschool calendars. The first is my yearly at-a-glance calendar. Here is what it looks like along with a few notes on how I use it:
I also keep a monthly calendar to which I can add field trips, birthdays, vacations, and other important dates.
When planning my year, I usually start with Christmas or Thanksgiving and work my way out. We do 4-6 weeks on and 1 week off except at Christmas and in summer. I usually start the first Monday in September.
Actually, this year we really won't have a stopping and starting point. I plan on just continuing what we are doing, and when we finish a book, we move on to the next one. We've had way more breaks this year than planned because of the new baby and some personal issues so I plan on schooling right through the summer (knowing that we will probably have lots of breaks in there for fun stuff - camping, day trips, etc). So our school year will "begin" in September but really it will mostly mean new school supplies and decorations in the schoolroom (also known as the living room - that's the price you pay for homeschooling 5 kids in a very small house).
You can download both of these calendars here.
The font used in the Excel version is called Space Woozies and can be found here.
The font used in the images above is called Sunshine Poppy and can be found here.