The minimum HCP to response comes from how high the opening hands can be. And secondly, what is the Game Points that you have agreed with your partner.
For example, your maximum point in that opening bid is 19 HCP. And your Game Points is 24 HCP. Then your “Minimum HCP to Response” is 24 HCP – 19 HCP = 5 HCP.
Meaning, when you have that minimum HCP, you MUST bid regardless of the quality of your hand. Why? Because your partner can have that maximum 19-HCP-hand. It could only need very little help to score an easy game.
This seems too obvious to write. But, you might hear someone says (hopefully NOT your partner), “Oh, but I got only 5 HCP and it was very bad.”
For example, your partner opens the bidding with 1♣ (3+card♣, 12-19HCP). Let us consider you have the hand below:
♠J43 ♥Q32 ♦J94 ♣J432 – (3-3-3-4, 5HCP)
Yes, not only it has only minimum 5-HCP, but it also has ~12 losers. And yes, you probably just want to pass. However, what if your partner has this hand:
♠AQT ♥A9 ♦QT ♣AKT986 – (3-2-2-6, 19HCP)
It would be quite easy 3NT, isn’t it?
So, next time you have this hand: ♠J43 ♥Q32 ♦J43 ♣J432, you know what to do: DO NOT PASS! If you do, prepare to find a new partner…