Can any of the devs explain me, how is the difficulty factor for the network calculated ?

If the difficulty is 300000, does it mean each Kekcoin got the chance of 1:300000 to win the next block reward ?

Would be great, if anyone could explain me how the difficulty factor is determined.

Planning to build a online staking rewards calculator and would like to use the actual probability of finding blocks.

Also is there any API for an average difficulty ?