Look at this investigation of "difficulty" to see how it is reducing every month for year over year to help determine if mining is profitable. You also need cheap power and the capital to buy a substantial amount of rigs:
This difficulty was reduced April 19, 2015 to 47,610,564,513. On Apr 17, 2014 the difficulty was 6,978,842,650. That means your hash rate, from April 17, 2014 to April 19, 2015 needed to increase 6.8 times to mine the same amount of coin. I plan on getting out WAAAAAAAAY ahead of the difficulty before the blocks halve and also have electricity rates of 3.4 cents per kWH to make the block halving much easier to bare if the price of bitcoin is the same as what it is today ($ 238.00).
EDIT: Sunday, May 3, 2015. Bitcoin difficulty on Apr 29 2014 was 8,000,872,136 [BTC-e $438.60]. On May 3, 2015 it was 47,643,398,018 [BTC-e $240.73]. That means the difficulty rose
5.95 times more than what it was a year prior. [Your hash rate would have to be 5.95 times more than what it was this time last year to mine the same amount of coin.]
So, if you had 10 TH/s a year ago, you need 59.5 TH/s today to mine the same amount of coin.Bitcoin difficulty on Apr. 17 2014 was 6,978,842,650 [BTC-e $485.58]. On Apr 19, 2015 it was 47,610,564,513 [BTC-e $220.43]. That means the difficulty rose
6.8 times more than what it was a year prior. [Your hash rate would have to be 6.8 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Apr. 05 2014 was 6,119,726,089 [BTC-e $467.78]. On Apr 05 2015 it was 49,446,390,688 [BTC-e $257.01]. That means the difficulty rose 8.07 times more than what it was a year prior. [Your hash rate would have to be 8.07 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Mar 24 2014 was 5,006,860,589 [BTC-e $588.71]. On Mar 22 2015 it was 46,717,549,645 [BTC-e $266.36]. That means the difficulty rose 9.3 times more than what it was a year prior. [Your hash rate would have to be 9.3 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Feb 17 2014 was 3,129,573,175 [BTC-e $612.00]. On Feb 22 2015 it was 46,684,376,317 [BTC-e $230.23]. That means the difficulty rose 14.9 times more than what it was a year prior. [Your hash rate would have to be 14.9 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Jan 24 2014 was 2,193,847,870 [BTC-e $774.98]. On Jan 27 2015 it was 41,272,873,895 [BTC-e $252.58]. That means the difficulty rose 18 times more than what it was a year prior. [Your hash rate would have to be 18 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Jan 02 2014 was 1,418,481,395 [BTC-e $782.00]. On Dec 30 2014 it was 40,640,955,017 [BTC-e $308.86]. That means the difficulty rose 29 times more than what it was a year prior. [Your hash rate would have to be 29 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Nov 29 2013 was 707,408,283 [BTC-e $1,019.60]. On Dec 02 2014 it was 40,007,470,271 [BTC-e $377.50]. That means the difficulty rose 56.5 times more than what it was a year prior. [Your hash rate would have to be 56.5 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Oct 26 2013 was 390,928,788 [BTC-e $171.37]. On Oct 23 2014 it was 35,985,640,265 [BTC-e $354.17]. That means the difficulty rose 92 times more than what it was a year prior. [Your hash rate would have to be 92 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Sep 25 2013 was 148,819,200 [BTC-e $122.55]. On Sep 25 2014 it was 34,661,425,924 [BTC-e $401.91]. That means the difficulty rose 232.9 times more than what it was a year prior. [Your hash rate would have to be 232.9 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Aug 24 2013 was 65,750,060 [BTC-e $106.34]. On Aug 31 2014 it was 27,428,630,902 [BTC-e $475.90]. That means the difficulty rose 417.1 times more than what it was a year prior. [Your hash rate would have to be 417.1 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Jul 22 2013 was 31,256,961 [BTC-e $84.50]. On Jul 25 2014 it was 18,736,441,558 [BTC-e $594.47]. That means the difficulty rose 599.4 times more than what it was a year prior. [Your hash rate would have to be 599.4 times more than what it was this time last year to mine the same amount of coin.]
Bitcoin difficulty on Jun 29 2013 was 21,335,329 [BitStamp $88.83]. On Jun 29 2014 it was 16,818,461,371 [BitStamp $599.86]. That means the difficulty rose
788.3 times more than what it was a year prior. [Your hash rate would have to be 788.3 times more than what it was this time last year to mine the same amount of coin.]
The numbers above reveal at one time we had as much as a
788.3 times increase in difficulty over a year's time. That number has reduced to
8.07 times more than what we had the year prior. The amount it increases year over year is being reduced every difficulty change quite significantly. I think now is the best time to get into mining than this time last year. I just started myself on September 22nd last year. By September this year, the difficulty might be around 64,000,000,000. That would be less than 2 times what it was September of 2014.
Like I've told others, I think I got in at the right time. I started out with 7 TH/s September 22, 2014. I ought to have 210 TH/s by September this year. That would be 30 times what I started out with September a year ago. However, the difficulty will have only come a little shy of two times year over year. I'm hoping to have 20 times that number in September of 2016 at 4,200 TH/s. And again, the difficulty might be 2 or 3 times what it was the year over year for September 2016 but I will have done a 20 times increase. I'll stop for a while somewhere in between 5,000 and 10,000 TH/s to recoup all of my investment and then some. Then start again...
If you look at the numbers below [curtesy of
https://bitcoinwisdom.com/bitcoin/difficulty] you can see what I see. For example: On
On May 24, 2014 the difficulty was 10,455,720,138. Do you honestly think it will be close to 10 times that at 100.4 Billion this coming May 24th of 2015? I seriously doubt it.
On Jun 29, 2014 the difficulty was 16,818,461,371. Do you honestly think it will be close to 10 times that at 160.8 Billion on June 29, 2015? I seriously doubt it.
On Aug 31, 2014 the difficulty was 27,428,630,902. Does one really believe it will be close to 10 times this at 270.4 Billion on August 31, 2015? I seriously doubt it.
Apr 19 2015 47,610,564,513 -3.71% 340,809,696 GH/s
Apr 05 2015 49,446,390,688 5.84% 353,951,052 GH/s
Mar 22 2015 46,717,549,645
-1.50% 334,417,246 GH/s
Mar 08 2015 47,427,554,951 1.59% 339,499,662 GH/s
Feb 22 2015 46,684,376,317 5.01% 334,179,783 GH/s
Feb 09 2015 44,455,415,962 7.71% 318,224,263 GH/s
Jan 27 2015 41,272,873,895
-6.14% 295,442,739 GH/s
Jan 12 2015 43,971,662,056 8.20% 314,761,417 GH/s
Dec 30 2014 40,640,955,017 3.00% 290,919,288 GH/s
Dec 17 2014 39,457,671,307
-1.37% 282,449,013 GH/s
Dec 02 2014 40,007,470,271
-0.73% 286,384,627 GH/s
Nov 18 2014 40,300,030,328 1.76% 288,478,854 GH/s
Nov 05 2014 39,603,666,252 10.05% 283,494,086 GH/s
Oct 23 2014 35,985,640,265 2.81% 257,595,247 GH/s
Oct 09 2014 35,002,482,026 0.98% 250,557,526 GH/s
Sep 25 2014 34,661,425,924 16.20% 248,116,151 GH/s
Sep 13 2014 29,829,733,124 8.75% 213,529,547 GH/s
Aug 31 2014 27,428,630,902 15.03% 196,341,788 GH/s
Aug 19 2014 23,844,670,039 20.86% 170,686,797 GH/s
Aug 08 2014 19,729,645,941 5.30% 141,230,307 GH/s
Jul 25 2014 18,736,441,558 8.08% 134,120,673 GH/s
Jul 12 2014 17,336,316,979 3.08% 124,098,191 GH/s
Jun 29 2014 16,818,461,371 24.93% 120,391,236 GH/s
Jun 18 2014 13,462,580,115 14.51% 96,368,902 GH/s
Jun 05 2014 11,756,551,917 12.44% 84,156,677 GH/s
May 24 2014 10,455,720,138 18.10% 74,844,960 GH/s
May 12 2014 8,853,416,309 10.66% 63,375,223 GH/s
Apr 29 2014 8,000,872,136 14.64% 57,272,474 GH/s
Apr 17 2014 6,978,842,650 14.04% 49,956,502 GH/s
Apr 05 2014 6,119,726,089 22.23% 43,806,706 GH/s
Yes, there is plenty of talk of the 3rd generation chips (rigs) coming out by the Summer of this year (2015). The power efficiency and hash rate of these 3rd generation rigs remains to be seen. Will 3rd generation rigs encourage miners who stopped mining to start back up again because of their power costs being above 15 cents per kWH? More than likely. Especially, if the price of bitcoin remains at the $235.00 to $335.00 level.
If bitcoin price is higher than $335.00 by the end of November, 2015, we could definitely see more miners wanting to come back into the fray. The only issue is will they be able to buy these 3rd generation rigs from those who will manufacture them? The demand for power efficient 3rd generation rigs could be quite high. The 3rd and 4th quarter of 2015 will be a very interesting time of year indeed for the miners.