Here is a chart that you can use that will help.
I have updated it with Bitmains latest offering of the Antminer S9.
It seems that the network difficulty will be dropping. Perhaps due to BCH taking a little of the mining hardware out of the picture or older hardware being taken offline to to operating costs.
To clarify the chart I have is set to have an increase in difficulty at 1% every 18 days. THIS IS AN ESTIMATE. It may drop % a few times. However I have factored in the average increase over the last two years and even the average from the last year.
https://docs.google.com/spreadsheets/d/11QS1BBV11KNGTF8N_-fdfmjTZ3WzPQFbLfVrl5n6R8s/edit?usp=sharing
https://i.imgur.com/v4xu4s1.pngGreat work, goes to show some naysayers here talking about Avg 15% increases... Some ppl are very naive to think big mining operations will run at a loss based on faith of a bitcoin price increase. Fact is mining will always be profitable, the only way a S9 becomes unprofitable is if something REALLY good is released in the next few months and they flood the market with it.