Real example: Avalon ASIC miner. Nowdays it can't mine shit for you. Despite it gave hundreds dollars a day to guys who bought it before May 2013.
Reason: the mining difficulty is rising up dramatically. See below.
The mining difficulty is rising up monotonously for ~20% every 2 weeks
Real example: this historical chart
(this chart updates every hour; source: http://divananalit.org/#Bitcoin-mining-difficulty-change )
Reason: I don't know. It's just happening at least for last year. It's like a Moore's law.
You can easy calculate will your ceх.io investment ever be in profit or not.
You can use simple formula of Infinite geometric series. For example, one GHS costs 0.0103 BTC. With current difficulty (6119726089.13) one GHS could mine 0.0011505 BTC per two weeks. If mining difficulty will rise up for 20% every two weeks, then reward will fall for 20% every two weeks, then the total amount of bitcoins we could mine with that GHS is:
0.0011505 / (1 - 0.8) = 0.0057525 BTC
But one GHS costs 0.0103 BTC — two times more expensive!
Conclusion: ceх.io is a chump investment. Do not buy anything there.
You can reckon will your ASIC miner ever be in profit if you'll buy it today
I'll just show you two things: "Mhash/s/$" characteristic which you could see in this table and this chart:
(this chart updates every hour and depends on current mining difficulty; source: http://divananalit.org/#Will-my-mining-investment-ever-be-in-profit.3F )
What conclusions could we make?
- Avalon (50 Mhash/s/$) bought today will pay itself only if you sell all gained bitcoins for thousands of USD.
- TerraMiner IV (333 Mhash/s/$) is already unprofitable
- Minerscube 15 (1666 Mhash/s/$) will make profit for you if you'll buy it today even if bitcoin price will fall down to $300.
Thanks a lot, be careful, use your brans. And sorry for my shitty language — I wrote a post in russian and decided to share this with you.