I should know this but in a different thread someone said the following:

How does one go about calculating this? In addition, I would be interested in seeing an excel spreadsheet if one is available where you can change {# of hands, winrate} to calculate the above.

Thanks in advance.

You need to know the standard deviation in addition to winrate. Although, you can probably just assume a stdev since most people's don't deviate too much.

OK, so, say you have someone's standard deviation in bb/100. A pretty standard example for NLHE would be 80bb/100. To find the standard deviation for *300* hands, it would be
S_300 = sqrt(3)*S_100
the sqrt(3) is because standard deviation increases with the square root of sample size. For 1000 hands it would be
S_1000 = sqrt(10)*S_100
and so forth. OK, so now we know that for the 300 hand sample, the standard deviation should be
sqrt(3)*80 = 138.5

You also want their win rate per 300 hands, which would be 3*-30 = -90

So now you use the excel function called NORMDIST.
NORMDIST(x, mean, stdev, cumulative)
in this case you'd use
NORMDIST(0, -30, 138.5, true)
Which decodes as... we have a person who is expected to win an average of -90bb (per 300 hands), with a standard deviation of 138.5, and we want to know how often he will end up at zero OR LOWER.

Since this returns the 0 OR LOWER, you'd subtract from 1. I get 25.7%, probably because I used different standard deviation than whoever you got the stat from. If you assume a stdev of 100bb/100 then I get 30.1%

From this I assume that the person you quoted was using a stdev of 110-115.

Typo here.

^Nice reply

You're right, sorry. The numbers/answers come from the right numbers though, I think.

Forgot about this thread as I've been swamped with work during the last several days.

Thanks for the awesome reply Rusty, plan to mess around with it more in excel soon.