The 15/25/35 Rule, Part 1: What is it?

The 15/25/35 rule is a tool that helps you determine whether you should cold-call a raise preflop with a speculative hand. It's based solely on effective stack sizes (and therefore implied odds (IO)). The 3-part rule states:

1. You need at least 15x the bet size in implied odds to call with a small/medium pocket pair
2. You need at least 25x in IOs to call with a suited connector
3. You need at least 35x in IOs to call with a non-suited connector or a suited gapper

For example, let's say you have a 4♣4♥ on the button in a $1/$2 and an UTG player opens for $6. Both you and he have $200 stacks. Your theoretical implied odds are therefore $200 / $6 = 33, which is greater than 15. Therefore, by the rule, you have enough IO to call and try to hit your set.

If your opponent had had a full $200 stack, but you only had $50 in your stack, your implied odds would have been $50 / $6 = 8.3, which is less than 15. Therefore you're not getting enough IOs to set mine.

Caveat: The 15/25/35 rule is just a guideline. The R-is-for-Reads step in REDi is vitally important to making this actually work correctly. For example, even if you're getting enough theoretical IOs, your actual IO's may be significantly less because your opponent isn't the type to pay off, or perhaps isn't holding the type of hand that he'll pay off with, etc.

All-in for now...
-Bug