I've made many times mistakes when it comes to 'full bet rule' when short stack is involved.
Are there any formulas, tips or rule(s) of thumb when it comes to this?

Situation:

P1 ($12): Call $0.50
P2 ($50): Raise $2.00
Hero ($50): ?

What would be the maximum-'minimum raise' that would not force me to call if P1 goes all-in?
I know that real minimum would be $3.50.

(2 - 0.5) + 2 = 3.50

Also, I'm confused how is P1 limp treated - it is in the pot but will it will be counted as part of all-in?

If you made it $7, a shove would be a minraise. Just work out what he'd have left if he called the current bet, and raise half of it.

I love that fact that you are looking at this 'rule'. I use it often in both directions to leave the door open for a re-raise or to try and trap callers into the pot should the short-stack shove.

But yes, 6-4 nailed it .. just remember that if the call amount is more than 50% of the remaining stack then the short stack will not be able to raise if they shove. GL

I am not understanding this part. Even if P1's shove does not represent a full bet, you can always fold.

The question that most people ask in this situation is 'What is the largest bet I can make where the short stack shoving would reopen action?' as they want to induce a shove from the short stack, get a call from the other player in the hand, then reraise. In that situation, SixFour covered how to size the bet so that a short stack shove reopens action to you.

But you are never forced to call a raise.

You need to make sure you understand the difference between a raise and a bet. In your action description, you say that P2 raise $2.00. This means that the bet to P2 was $.50, and P2 raised $2 more to make the bet $2.50.

What you mean to say is that P2 raised $1.50 to $2. I am not trying to be nit picky or pedantic, but it matters when you start talking about minimum bets or reopening action what the raise was.

As far as P1's limp, any bet made is already part of the pot, and P1 is only responsible for the amount that is raised to him. So P1 limped .50, P2 raised $1.50 to $2, and P3 raises $5 to make it $7. Now, P1 is facing a raise of $6.50 (p2's raise of $1.50 plus P3's raise of $5). They can fold and relinquish any claim on the pot, but they do not get any bet they have made back. If he raises, action is open to P2 and P3. If he only calls, action is open to P2 (since P3 raised him), but not open to P3(unless P2 raises)

FMP .. GL

Sorry for my ignorance, I don't understand what you are saying here. I thought that anything above one big blind is considered a raise, and the other players are allowed to reraise afterwards. On what site are you playing with this rule of 50% of the stack, or is it a live poker thing?

That’s not true anywhere I play, both live or online. An all-in where the raise isn’t at least the size of the last raise doesn’t re-open the action for anyone who wouldn’t have another action if the all-in player had called instead.

Example:
Player 1: raise to 10
Player 2: raise to 20
Player 3: all-in 21
Player 1 can fold, call or fold. If he calls or folds, player 2 can call or fold but not raise. If player 1 raises to 30 or more, player 2 can fold, call or raise.

Thanks, I was not aware of that, even though I've been playing online for a while. Yet another example of how dumb I am.

Player 1 has 100 in stack

Player 1 bets 20 .. leaving 80 behind

Player 2 raises to 61 .. a raise of 41

Player 1 goes all-in for 100, but only raised 39 .. so Player 2 (and any other Player who called the 61) may not raise, only fold or call the 100

Since the call amount of 41 is more than 50% of Player A's remaining stack, Player A can't reopen betting by going all in. GL