The Bitcoin confirmation time - the time it takes to mine a block of Bitcoin transactions - fluctuated by several minutes over the course of February
Table of contents
- How Bitcoins are Transferred
- Bitcoin (BTC) block time from 2017 to March 28, 2021
- How to Check Bitcoin Confirmations
- How long does it take for a Bitcoin transaction to be confirmed? - Coin Center
Unfortunately, the blockchain does not offer strong consistency , meaning that any data included in the blockchain is guaranteed to be included forever. For technical reasons, the blockchain offers a weaker property called eventual consistency , meaning that eventually all parties will agree on the blockchain up to a certain ever-increasing prefix.
Put another way, the blockchain is a series of n blocks currently almost , , and at any given time the most recent several blocks are not guaranteed to be permanently included. It is possible for the blockchain to fork by having multiple potential often inconsistent blocks which claim to be the last block in the chain.
When an apparently valid block is replaced by a competing block, this is called a blockchain reorganization and the replaced block is called an orphan block. However, it is possible although rare for the last n blocks to be orphaned in a reorganization. This is exponentially less likely to occur the larger n gets. It typically happens multiple times a day, for example, that a single block is orphaned, but has happened only a few dozen times in history for n between 2 and 4, and exactly once for n greater than 4 a block reorganization in March due to a technical glitch.
Barring technical glitches, formal modeling of Bitcoin suggests that large reorganizations are exponentially unlikely, but possible. In practice, the community has adopted 6 blocks as a standard confirmation period. For relatively small transactions like buying coffee , users might be fine with a shorter confirmation period such as one or even zero blocks. Assuming Alice is fine with the community standard of 6 blocks, how long will she have to wait? Because blocks are found by a random process, there is no telling precisely how long it will take for 6 blocks to be found.
On average, it takes about 10 minutes to find each block.
How Bitcoins are Transferred
The average block time can actually be slightly shorter or longer depending on if the total hash power of the Bitcoin network is growing or shrinking. Ignoring this detail though, this is why 6 confirmations take about 1 hour on average. However, the block-creation or mining process is random and each block may take much longer or shorter. But in practice, since the computational power thrown into the bitcoin mining improved vastly, the time takes to mine a block is kept at a constant number which is 10minutes , by increasing the level of difficulty.
During the first five years of bitcoin, the difficulty level increased from 1 to 50 billion. In each block, in the header there is a parameter called, bits — and in the genesis block the value of bits is This is a compact format — which can be used to find the target hash value for this current block.
Bitcoin (BTC) block time from 2017 to March 28, 2021
In fact the hash of this block must be less than or equal to the target. The value of the target is calculated only after blocks, along with the difficulty level calculation — and once calculated the next blocks will cary the same value in its bits block header parameter. The first two digits of the above hexadecimal value is known as the exponent , which is 1D and the next six digits 00FFFF are known as the coefficient. Now if we apply these value to above function, it will look like the following.
Converted that into decimal would be 2. To make it much clear — since the hash of the block must be in bits — lets also represent the target in bit by adding leading zeros. Now the hash of the genesis block must be less than or equal to the above, which is:.
As we explained before, the difficulty of the genesis block is 1. After every blocks, the target is recalculated in the following way. The difficulty is calculated in the following way:. For example, the new level of difficulty for the th block is calculated in the following manner:.
This is just an assumption — in reality the level of difficulty of the bitcoin blockchain remained same till the th block — and only changed from 1 to 1. Now, if we add leading zeros to make the above number, then the target will be:. The new target is less than the previous one — so the mining software has to find a nonce value, which makes the hash of the block less than or equal to the above.
When the computational power increases, the average block time decreases — and then the difficulty level increases by having a low target value. The next blocks will carry in the block header, the value of the new target as the bits parameter — and the value of the new difficulty level as the difficulty parameter. Once you cheat and then send the copy of the mined block to others, other legitimate miners who validate the block will find its not done properly and reject it.
The miner who cheats then will automatically fall into his own copy of the blockchain.
The int function returns the largest integer less than or equal to a given number. If you look at the above formula, it has two main parts. The first part to determine how much the block time deviates from the expected block time 10 to 19 seconds. If current block is mined faster, in less than 10 seconds, then this factor will be positive number, which will increase the difficulty. It will result in a minus value when the block time is greater than or equal to 20 seconds, and the difficulty will be decreased but still will have the impact of the difficulty bomb, which we will talk later.
The second part of the above formula is known as the difficulty bomb. This will only impact if the block number is greater than So, the total difficulty will be. Note : Frontier, the initial release of the ethereum, pushed live in July , was targeting to keep the ethereum block time around 12 seconds. The above discussion is related to the homestead ethereum release — not the frontier.
Following shows the difficulty calculation used in frontier. So, to keep ethereum block time at a considerable level, the computational power also must increase with the time to match the difficulty bomb — if not, it will be hard to mine ethereum, which will result in a ethereum blockchain freeze — also known as ice age.
The ethereum difficulty bomb, which makes mining harder with an exponentially increasing difficulty level over the time was introduced to discourage the miners to continue mining with proof of work mining, when the ethereum serenity release in the future introduces proof of stake mining.
How to Check Bitcoin Confirmations
The difficulty level was introduced with the first patch to the ethereum frontier. Frontier was the initial release of ethereum, pushed live in July As we discussed in the previous section, following is the change bold introduced to ethereum difficulty algorithm to support the difficulty bomb:.
Note that, the above algorithm is based on the ethereum homestead release, not from the frontier release, where the difficulty bomb was introduced. Anyway, between these two releases, even though the difficulty algorithm got changed, there was no change to the difficulty bomb part. I don't think you understand what a Poisson process means. It does NOT mean that there is a constant time interval in between events.
It means that it is a random process in which events are independent of each other. There is an average time interval, but this is by no means constant and it is NOT even the same as the "expected" time interval. The bitcoin difficulty is designed to have an average interval between blocks of about 10 minutes. I have made a table below, showing what this means if you take Poissonian statistics into account.
How long does it take for a Bitcoin transaction to be confirmed? - Coin Center
It shows the percentage of transactions are are expected to complete within the specified number of minutes. The way to rationalize this is simply to understand that the process is random--so some intervals will be longer than others. And since it is possible for some confirmations to take place very soon after each other, then obviously some confirmations will be very far apart in order to "justify" the average interval between confirmations.
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