What used to take me 1 day to mine now takes me four months. That is the difference of one year.
This time next year will it be the same difference? What has the trend been year on year?
Difficulty is going to continue to rise as more miners mine and more miners replace/add faster equipment. There's talk of it leveling off some day in the future, I think there are too many factors to take into consideration. To keep up, it's simply a matter of adding Gh/s right now with balancing costs.