As I have mentioned before on this blog, I have noticed a repeating patten in the Mac OS’s acquisition of market share. Every first half of the year, usually from January to July, Mac OS market share stays steady, with occasional small ups and downs–but then, starting in August, it rockets upwards and keeps going until December. (Note in the chart below: light blue denotes the late-year growth season, darker blue denotes the early-year doldrums.) And so far, this pattern, which I noticed a few years ago, has held true.

Currently, the Mac OS is hovering less than 10%; if the past trend holds true, we’ll be seeing the Mac market share rise to 11.5% or 12% by December 2009.

I made a similar prediction almost exactly a year ago, guessing that the Mac market share could jump to anywhere from 9% to as high as 10%. Seeing the graph above, you can confirm that I was pretty much right on target: the Mac’s share stopped just shy of 10%. My prediction the previous year that the Mac OS would have an 8% share by the start of 2008 was a bit high, but close–it topped out at about 7.6%. So I am fairly confident that by January 2010, we could be seeing a 12% share, and a year later, maybe 14%. This also would track with my prediction in 2007 that we’d see the Mac market share rise to between 12% and 15% by 2010. As I mentioned before, if that trend continues, Apple could have 30% of market share by 2015–ten times what it had in 2005.

Also, at this rate, the iPhone is set to overtake Linux as an OS by the end of 2010.