This is incorrect. 50% of the mining power gives you 50% probability of finding the next block.

This will probably make newbies or those who doesn't know believe that those who have 50% mining power have a 100% probability of mining the next block if not because of the explanation above. I would say that if you have 100% mining power then I could say that it is possible to have 100% probability of mining most of the block. I just checked mempool.space and foundry USA pool have more mining power which have more chance of mining ntje next block.

Sorry I have to delete what I posted about this before. This is not about a miner to mine the next block alone. Two miners can mine a block, first, the two blocks are valid, but one will become invalid after chain reorg. The miner that finally mine the (valid) block is the one that mined the block that other blocks are building on after chain reorg to have the longest chain.

A block can be mined by two miners, let us assume by a miner A with 40% hashrates and miner B with low % of hashrates. In such a way if 2 blocks are mined at the same time, there would be a chain reorg in a way new blocks mined will build on the longest chain which will be valid while the other become no more valid.

With a single miner having 40% of the hashrates, the miner would mine more blocks and have more chance to compete with other miners with low hashrates during chain reorg, so having more chance to be the miner that will finally mine the block, while chances that blocks mined by other miner become invalid is higher.

But the longer the chain by uncentralized miners, the lesser the chance.

You can check the table in the OP, having a hashrate of 40%, there is 73.6% chance that the miner can replace (finally be the valid block mined) blocks with 1 confirmation, 66.4% chance to replace block having 2 confirmations already...33.2% chance to replace block with 10 confirmations.

Having 50% hashrates should be able to lead to an attack in a way the chance to reverse 10 blocks should be possible, but the more the centralized hashrate, the easier the chances of the attack.

Nope, it doesn't, the probability for the next block is the same, you can't have 100% probability on the next block even if you own 99.9999% of the hashrate.


And the OP should have also added the tiny writing under that table:
It's not about mining the next blocks faste than others is about mining a longer chain others don't know about.


Taking away 51% of the hashrate and having it mine in secret a second chain is close to impossible right now, not with 20% of the hashrate in hands of public traded companies (with more to come) that will not only be the first going bankrupt but will also face lawsuits after lawsuits from this.

The topic title indicates "Bitcoin 51% attack and its effect " but you didn't talk about the effects, I can quote the effects from here ---> https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power:



I think that the percentages mentioned above are not accurate, you can find more here  https://bt.irlbtc.com/view/2227.msg30083#msg30083 .


Personally, I don't see that someone who would attempt such a costly attack would attempt to do so at a rate of less than 60% and would rely on luck while burning millions of dollars every second.

You are calculating the percentage chance for a malicious miner to overcome an x block deficit and catch up to the main chain. The table OP has lifted from learnmeabitcoin calculates the percentage chance for a malicious miner to overcome an x block deficit and overtake the main chain by 1 block. If you add 1 to your z value for all your calculations, they'll match the table on learnmeabitcoin.

I'm not sure what OP has done, but all his numbers differ from the actual calculations on the table he is copying. I think it's safe to say he doesn't understand what he is posting.

You are correct, but catching up to the main chain as opposed to overtaking it is the definition that Satoshi used in section 11 of the whitepaper, so that is what has stuck.

Correct, which matches the table at the bottom of the page on learnmeabitcoin that OP listed as his source here: https://learnmeabitcoin.com/technical/51-attack. As I said, OP has (for reasons unknown) slightly changed all the numbers to incorrect ones.

Thank you all for the corrections. With all your replies so far, have seen where my lapses where and I will take them into consideration when making a new thread in the future.
Thank you all for your contributions, am going to lock this thread now.