One week of mining at 20GH/s will get me about $180 in a month considering I've made $46 in a week or $540/month with both blades and the BFL unit mining in parallel (considering no difficulty increase). At this rate I will brake even in 6 months but my goal was to hold onto my bit coins and pay off my investment with fiat money. It is a risk I was willing to take from the start, I've made much worse decisions before...
But, don't you know that the difficulty is increasing about 30% every 11 days? Do you understand what effect that will have on your earnings?
You say you currently make $540 per month, or roughly $18 per day. Over the next 11 days you will make $180, and then you will make 30% less, or $126, over the following 11 days, and so on. Let's look at what you will make (rounded to the nearest dollar):
| Days | Income | Total Income |
| 11 | $180 | $180 |
| 22 | $126 | $306 |
| 33 | $ 88 | $394 |
| 44 | $ 62 | $456 |
| 55 | $ 43 | $499 |
| 66 | $ 30 | $529 |
| 77 | $ 21 | $551 |
| 88 | $ 15 | $565 |
| 99 | $ 10 | $576 |
| 110 | $ 7 | $583 |
| 121 | $ 5 | $588 |
| 132 | $ 4 | $592 |
| 143 | $ 2 | $594 |
| 154 | $ 2 | $596 |
| 165 | $ 1 | $597 |
| 176 | $ 1 | $598 |
| 187 | $ 1 | $599 |
After 6 months, you will have earned only $600, not $2500.
Thank you for breaking it down, I had no idea that difficulty goes up this dramatically so fast. Time to get rid of the miners then...
Keep in mind that these numbers are probably not accurate. The difficulty has been going up at this rate for 8 months now, but it can't keep going like this forever. Eventually, it will have to slow down and it is not clear when that will happen.
My actual prediction is that the difficulty will continue rising at this pace for another 3 months before its starts to flatten out. I predict that it will go up an average of 20% every 12 days in the end, and each GH/s mining now will earn a total of less than 0.14 BTC. It is not quite as dramatic as the table above, but your 60 GH/s will earn only 8.4 BTC, which is less than what you paid.
