From this
How many Bitcoin confirmations is enough? with open source code from Jameson Lopp that is built with formula from Bitcoin Whitepaper.
to that finding from a forum member @o_e_l_e_o
His numbers are actually a little off.
For 33.55% of the hashrate, the probability an attacker is successful after 1 confirmation is 70.12%, after 3 confirmations is 43.54%, and after 6 confirmations is 23.09%.
On closer
examination of the code here, it seems the error is that his calculation is not taking in to account fractions of a percent. You can test this yourself by putting in the hashrate box, for example, 30 and 30.999, and seeing they produce the same result.
Anyone can build your tool but without that bug?
Community will have a more accurate tool to use.