Bitcoin halving facts

One of Bitcoin’s primary selling points has been its finite supply. Akin to gold, a limited amount of Bitcoin can ever reach circulation, and nothing on this world can change that. To continue the gold analogy, some Bitcoin are in circulation, while others have yet to be mined. We know they exist, but they are only ‘released’ in slow intervals over the next decades. Every 10 minutes in average a new Block is mined, and this block contains newly minted Bitcoin, the reward. Every 210,000 blocks (4 years minus 64 hours) a new epoch starts, and the reward is slashed in half.

1. For each epoch, the block reward is equal to the percentage of Bitcoin mined
   The emission schedule follows a simple geometric series (see above). That means it has some convenient properties. Satoshi likely chose the block reward so that in each epoch, the reward is equal to the percentage of Bitcoin mined in that epoch. E.g. in the first epoch, the block reward was 50 BTC, meaning 50% of all Bitcoin were mined in that epoch. The upcoming 4th epoch will have a block reward of 6.25 BTC, meaning 6.25% of all Bitcoin will be mined in the coming four years.
2. In each epoch, exactly as many Bitcoin will be mined as in all epochs after
   Following the properties of the geometric series, the block reward of a single epoch is as large as all Bitcoin mined after it. We are about to reach the end of Epoch 3, with a block reward of 12.5*210,000. Therefor, 2.625 million Bitcoin will be mined in all epochs after. Similarly, in epoch 24, starting 2101, 1.25 Bitcoin will be mined in total, meaning that in all 8 epochs after, only 1.25 Bitcoin will be mined as well.
3. Due to a rounding issue, there won’t be exactly 21 million Bitcoin
   As a Bitcoin is only divisible into eight decimals, we cannot indefinitely half the block reward. Starting with epoch 11 (2049), we for the first time have to round down half a Satoshi per block. From epoch 30 to 31, the block reward drops from 9 Satoshi to 4 Satoshi, a full 55% drop. In total, only 20,999,999.9769 Bitcoin will be mined.
   Additionally, many of the later block rewards might not be spendable, at least not with the (hopefully hefty) opportunity cost of kicking other transactions out of the block.
4. We’re way ahead of schedule
   Due to rapid increases in hash power, the average time between epochs has been shorter than the expected 1458 days. Epoch 1 ended 33 days early, epoch 2 ended 139 days early, and epoch 3 is expected to end 55 early. In sum the Bitcoin release schedule is 227 days early.
5. By 2033, 99% of all Bitcoin will have been mined.
   In only 13 years, 99% of all Bitcoin will have been mined.
6. Also: The halving sounds like Hal Finney

This is how bitcoind tests the total amount of Bitcoin

The halving has more of a psychological than economical or technical justification. A continuous reduction of the Bitcoin block reward would have the same effects, but wouldn’t provide us with an opportunity to come (virtually) together, celebrate, blog and talk about Bitcoin’s economics.

In this geometric series, the total area size is 2.

Halving #3

The third halving is expected to occur around 12 May 2020. We invite you all join to the Bitcoin Association of Hong Kong to celebrate this event with Bitcoin Magazine and friends from all over the world with a 21h live stream.

You can find more information about the event here and specifically about Hong Kong’s participation here.