Transaction confirmation

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Transaction confirmation is needed to prevent double-spending of the same money. One of the main advantages of bitcoin is that it avoids the problem of double-spending, i.e. the risk that a digital currency token may be copied and spent more than once. In spite of having no central authority to verify that its tokens are not being duplicated, bitcoin successfully avoids double-spending through a system of decentralized transaction confirmation, based on the consensus of its users. Bitcoin transaction time is always changing and it depends on the miner's fee.

How to confirm bitcoin transaction?[edit]

A transaction is a transfer of value between Bitcoin wallets that gets included in the block chain[1]. Bitcoin transactions are not immediate. When a user wishes to send bitcoins, information is broadcast from her wallet to the (users in the) network, who verify that she has enough coins, and that they have never been spent before. Once validated, miners will include this transaction – along with others – in a new block in the blockchain. This is called a transaction confirmation. The transaction is now said to be "unconfirmed bitcoin transaction".

Each time a new block is added to the chain (every ten minutes), the transaction is said to be confirmed again. As a consensus, many users wait for a transaction to be confirmed six times (after roughly sixty minutes) before accepting it as payment, to avoid double-spending. Users will usually show a transaction as "n/unconfirmed" until it is six blocks deep.

Example of the transaction confirmation time

Bitcoin confirmation time[edit]

The deeper a transaction is buried, the harder it will be to manipulate. Although 0/unconfirmed transactions could be reversed via Finney attack, race attack, or 51% attack, small amounts of money will not be worth the trouble. Larger sums are worth protecting under more bitcoin confirmations. The number six is just an arbitrary limit, beyond which the feasibility of an attacker being able to amass more than 10% of the network's hashrate for purposes of a transaction falsification becomes negligible (a risk lower than 0.1%).

Each additional confirmation is a new block being found and added to the end of the blockchain. Miners create blocks by solving the proof of work for their proposed block. The block interval has an average of 10 minutes but not every block interval is exactly 10 minutes. It follows a statistical process known as a poisson process, where random events happen with the same probability in each time interval. Another way of expressing this is that the mining process has no memory, at every second a block has the same chance of being found. Poisson processes are well-understood but can be unintuative.

There are lots of block intervals with a time less than 10 minutes but then a few block intervals much longer which bump up the average to 10 minutes. So the bitcoin network can get unlucky and a block won't be found for a whole hour.

In a 10 minute interval, the probability of a block being found is about 63% (or 1 - e^(-1)). So approximately two-thirds of the time a block will be found in 10 minutes or less. In 30 minutes a block has a 95% chance of being found, which rises to 99.7% if the time interval is 60 minutes.

Having understood how transactions occur, you should find out what affects the speed of processing and verification of information. To speed up the process, you need to know that it can slow down. Usually at the final time is affected by:

  • network utilization;
  • sharp jumps in the course;
  • low commission.

The influence of the first factor is especially noticeable. When the system needs to process many requests, users have to wait. Especially long we have to wait in the days of peak activity, which is not often, but sometimes. Of great importance is the Commission paid to miners. The bigger it is, the higher the priority will be. The size of the transaction also has an additional impact: sending large amounts is much faster.

How many confirmations in bitcoin needed?[edit]

Although six confirmations is the consensus, merchants and exchanges that accept bitcoin as payment for their products and services should set their own standard of confirmations they require before accepting payment.

Freshly-minted bitcoins can only be used after 100 confirmations, to prevent coins from orphan blocks being spent. Older bitcoin client will not use newly-earned coins until they have 120 confirmations.

Number of Confirmations[edit]

How to Confirm a Pending or Stuck BItcoin Transaction

The classic bitcoin client will show a transaction as "n/unconfirmed" until the transaction is 6 blocks deep. Merchants and exchanges who accept bitcoins as payment can and should set their own threshold as to how many blocks are required until funds are considered confirmed. When potential loss due to double spending as nominal, as with very inexpensive or non-fungible items, people may choose not to wait for a transaction to be confirmed, and complete the exchange as soon as it is seen on the network. Most exchanges and other merchants who bear the risk from double spending require 6 or more blocks.

To find out how many checks are required to process the transaction and how long to wait for the receipt of funds, it is necessary to understand the features of cryptocurrency transfers. This process consists of several stages:

  • addressee sends money;
  • information about transactions is made in special blocks, each of which has a room and a hash (special data);
  • the blocks are sent for scanning to different computers;
  • if everything is done correctly, the received information replenishes various databases;
  • checked blocks complete the chain;
  • the money goes to the recipient.

To make a transfer, the transaction must be verified in 6 blocks. If this does not happen, cryptogenic reach the final destination. Accordingly, the speed of confirmation depends on the time of sending Finance.

There is nothing special about the default, often-cited figure of 6 blocks. It was chosen based on the assumption that an attacker is unlikely to amass more than 10% of the hashrate, and that a negligible risk of less than 0.1% is acceptable.Both these figures are arbitrary, however: 6 blocks are overkill for casual attackers, and at the same time powerless against more dedicated attackers with much more than 10% hashrate.[2]

Freshly-mined coins cannot be spent for 100 blocks. It is advisable to wait some additional time for a better chance that the transaction will be propagated by all nodes. Some older bitcoin clients won't show generated coins as confirmed until they are 120 blocks deep.

How Many Confirmations Is Enough[edit]

Transactions with 0/unconfirmed can be reversed with not too much cost via Finney attack and race attack, but in some cases may still be acceptable especially for low-value goods and services, or ones which can be clawed back.

For transactions with confirmations, the website ( can be used to calculate the probability of a successful doublespend given a hashrate proportion and number of confirmations. Note that in the reality of bitcoin mining today, more than 6 confirmations are required. (60 confirmations to have <1% odds of succeeding against an entity with 40% hash power). See Section 11 of the ( bitcoin whitepaper) for the AttackerSuccessProbability formula.

Some mining enterprises may hide their hash power across several mining pools. Also mining ASICs can be temporarily overclocked to increase their hash power. This is less power-efficient but could be used for a brief burst of hashrate. For maximum safety, it is recommended that for the irreversible sale of items with value comparable to the block reward, a large number of confirmations (144 blocks = 1 day) is required before completing the exchange.

See also: Irreversible Transactions

Bitcoin transaction accelerator[edit]

Theoretically, it is impossible to speed up the confirmation of bitcoin transactions. Because it is impossible to increase the speed of data processing on another computer. But the reality is somewhat different. Cryptocurrency holders can take advantage of several options:

  • the increase in the size of the commission;
  • using proven reliable wallets;
  • the opening of the transaction;
  • using multifunction purses that support the creation of multipurpose.

Additionally, visitors can use the alternative, involving the procurement transaction as a reserve. This option requires the creation of a private, independent from the wallet address bitcoins.

Depending on conditions the time of making the bitcoin payment can be both immediate and delayed for a few days. Therefore, in order not to be in a difficult situation, you should think in advance about all the details and decide how to speed up the process. And the most important is the size of the Commission and the reliability of the selected wallet. If miners get a good reward, the priority of data processing will increase dramatically. A high-quality payment resource is able to make a financial transaction instant.

See also[edit]

External Links[edit]


  1. n.d., How does Bitcoin work?,, n.d. Retrieved 02/03/18.
  2. Analysis of hashrate-based double-spending