Update September 14th 2013

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And as always here is the link to the updated estimate both 20% and 30% increases.

Estimates of so low (20%-30%) difficulty increases are pretty much useless. With all these hardware being delivered even 40%-50% difficulty increases may be unrealistically low.

These are 10.7 day increases, not monthly increases.

10.7 days is equivalent to 30% increase.

I am doing 12 days 20% for a minimum estimation of what to expect.

IT has been evident that 30% is the new norm. However 20% is the yearly average. Come October the minimum will probably be 30% or every 10 day network difficulty change.

Many new potential miners are being left in the dark to the simple fact that network difficulty reduces return in a substantial way.