How the steamgifts calculate Probability of Winning Per Day?

(Number of copies * 1) / number of entries (100)

that's for a single giveaway, the thing per day i assume is counting every giveaway joined that day

1 - probability of winning nothing (product of (1 - (number of copies)/(number of entries)) for each giveaway you entered), I guess.

It just simply calculates your odds of winning based on what you have entered.

If you are the only person in a giveaway, you will 100% chance of winning on the day that giveaway ends. As soon as a second person enters that giveaway your odds will drop to 50%. When there are 100 people, your chance will drop to 1%. It adds up the odds of every giveaway for each day and then gives you a total chance of winning for each day.

It rounds to a whole number though, so if you have less than 0.5% chance of winning on a given day, it will show 0%.

Let n denote the number of giveaways you entered. The indices are i in {1, ..., n}.

The numbers of copies are c_i. The number of entries are e_i.

The probability to not win a certain giveaway i is Pr(not win i) = 1 - max(c_i / e_i, 1).

The probability to not win any giveaway is Pr(not win 1, ..., n) = Pr(not win 1) times Pr(not win 2) times ... times Pr(not win n).

The probability to win at least one giveaway is hence 1 - Pr(not win 1, ..., n).

ok everyone,thanks