There is no exact rule to determine how long a period that makes a lotto number cold. It varies from one game to another. However, using Statistics, we can get an idea when to consider a lotto number cold.
For Grand lotto 6/55 specifically, a lotto number turns cold after 10 to 15 draws that it has not been winning. If a lotto number has not won for the last 9 draws, that number may or may not turn cold. There are many cases when on the 10th to 15th draw, the number may win again. However, if the number remains non-winning after the 15th draw, the number tend to hibernate or sleep. That means, it remains non-winning for a longer period. On record, the number 27 hibernated for as long as 67 draws. The shortest hibernation period is 27 draws.
Should you bet on cold numbers?
If a number has not been winning for 9 consecutive draws, that number may turn cold. But there is also a possibility that it may immediately win within the next 6 draws (10th to 15th draw). If after the 15th draw the number has remained non-winning, most likely this number will sleep or hibernate. In that case, might as well not play on that number.
So, the answer is 'yes' if the number has been cold only for 15 draws. 'No' -- if the number has remained non-winning for longer than 15 draws. The shortest hibernation period is 27 draws -- that is equivalent to 9 weeks. So why risk playing a number that is unlikely to win for a long period of 27 to 67 draws?
Which numbers are hibernating today?
As of June 22, 2012, the numbers 18 and 37 have been hibernating. The number 18 has been asleep for 59 draws now. It has not won since Feb 1, 2012. The number 37 has been asleep for 23 draws now. It has not won since Apr 28, 2012.
The numbers 2, 3, 7, 25, 35, 39, 41, and 49 are considered cold numbers currently. They have been cold (or not drawn) for the last 11 to 15 draws. At any time, any of these numbers may win again or it may continually to hibernate.