Bitcoin Forum

2009-2012(December)(close to 4 years) = 210,000 blocks = 10.5 million BITCOINS

QUESTION 1. Why would it not be exactly 4 years? Is it because of the exact month that the genesis block was mined in?

2012-2016 = 210,000 blocks = 5.25 million coins

2016-2020 = 210,000 blocks = 2.625 million coins

2020-2024 = 210k blocks = 1.3125 million coins

2024-2028 = 210k blocks = 0.65625 million coins/656,250 coins

2028-2032 = 210k blocks = 0.328125 million coins/328,125 coins

2032-2036 = 210k blocks = 0.1640625 million coins/ 164,062.5 coins

2036-2040 = 210k blocks = 0.08203125M coins/ 82,031.25 coins

2040-2044 = 210k blocks = 0.0205078125M coins/ 20,507.812 coins

2044-2048 = 210 blocks = 0.01025390625M coins/ 10,253.90625 coins

2048-2052 = 210k blocks = 0.005126953125M coins/ 5,126.953125 coins

2052-2056 = 210k blocks = 0.0025634765625M coins/ 2,563.4765625 coins

2056-2060 = 210k blocks = 0.00128173828125 M coins/ 1,281.73828125 coins

2060-2064 = 210k blocks = 0.000640869140625 M coins/ 640.869140625 coins

The network targets 1 block every 10 minutes.  So if the network was exactly on target 210,000 blocks = 1458 days and 8 hours.  4 years is 1461 days (including 1 leap day) so it is just short of 4 years even under optimal conditions.

However the network is always estimating the difficulty needed to maintain 10 minutes per block and due to changes in hashing power the network can slightly over or under perform that target resulting 210,000 blocks taking more or less than 1458 days and 8 hours.

The reason it's not exact is because as more mining power comes online, it pushes each set of 2016 blocks to be completed faster than 2 weeks. This cuts out a small amount of time from the 4 years total. In the past month you could watch the exact time for the halving creep sooner.

It would go farther out if less people were mining, and this was seen in bitcoin in late 2011 as the difficulty dropped, and has also been seen in alt currencies.

The difficulty algorithm uses the mining power of the previous period to compute the difficulty of the next period, and assumes that the power does not change. So, if the power increases during the next period, the blocks will be generated faster than planned. If the power decreases, the blocks will take longer than planned.

These two events should have an interesting effect on block generation times: reward halving and the introduction of ASICs.

The difficulty just changed today and the reward halves in two days. When the reward drops, the mining power is expected to drop significantly. Block generation will take much longer until the next change in difficulty. The duration of the current difficulty will be much longer, too.

When ASICs come online, the mining power will rise dramatically and blocks will be generated much faster than normal. The difficulty will change much sooner than normal, too.

Good explanation, i've always been wondering about this.

Genesis block was mined in November 2009 if I recall? It would've been a 4 year cycle if not for rising difficulty as a result of blocks being found at a rate faster than once every 10 minutes. Thanks to our difficulty of 3,438,909, the cycle lasted about 3 years, not 4.

January 3, 2009 18:15:05 (http://blockchain.info/block-index/1/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f) so yes, it's almost been 4 years.