When I play with friends live poker we always ask ourself what are the min-raise and min-reraise rules in Holdem No Limit?
First off, make sure not to call a "bet" a "raise". If you can check, that is you aren't facing an amount you have to call, then when you put in chips it is called a bet. If you have to put in some amount of chips to continue with the hand, and you want to increase the pot, it's called a raise. If it is confusing, just remember this old poker adage: "You can't raise yourself."
In No-Limit Hold'em, the minimum bet is usually the big blind. The minimum raise is going to be the amount of the previous bet or raise called. For example, in a 1/2 nl game, the minimum you can raise before the flop is going to be to make $4... you are calling the $2 blind and then raising $2. If you make it four, the next player to act can raise to a minimum of $6... remember you are only raising $2.
This can get tricky when a player is all-in. Keep in mind that a player can always push his whole stack into the middle in NL, even if his stack is less than what a min-bet or min-raise would be. The question that arises often is whether a shortstack shove reopens the action to an original better.
For example, let's say you are playing NL holden with blinds at 100-200. You are first to act after the flop and you bet 500. A shortstacked player then shoves all-in for 700. Two other players call behind him. Now it's back up to you and you want to reraise. This scenario leads to arguments all of the time and I've seen lots of floor staff get it wrong.
Rules are going to be different from place to place, but under the TDA rules, it opens up the action again to you if the shortstacked player's raise is at least 1/2 the minimum. So in the example I gave, the shortstacked player would have to have made it 750 for you to be able to reraise when it got back to you. Other places don't use the 1/2 minimum rule and won't let the action be opened back up unless the full minimum amount is met.
Here is Rule 41 of the TDA :
Limit games are very tricky with this. If in a 3/6 Hold'em game, player A bets $3, and player B goes all-in with $4, then player C has the option to call the all-in, complete the raise to $6, or fold. If player C completes the raise to $6 then player A may call the $6, fold, or reraise to $9.
Now, on the flip side, if player A bets $3, and player B goes all-in with $5, then player C has the options of folding, calling the $5 all-in, completing the raise to $6, or realising for a total of $8 ($3 more than the all-in). Furthermore, If player C only calls the $5, player A still has the option to reraise to $8 or complete the raise to $6, forcing player C to put in more money to continue with the hand.
Thus details the "1/2 or more rule"
For no-limit games, in either of these scenarios, player C may only call the all-in or fold. Because the all-in was not a full raise, reraises are out of the question.
Disclaimer: This is the way that it is done at the casino where I work, where you play may have different rules.
This can vary. In a lot of European card rooms the minimum raise is the size of last bet, not the size of the last raise. So let's say in a 1/2 game you raise to 6, then someone else reraises to 12. In many European rooms the minimum bet for you to raise now is 24, while in most US rooms it would be 18.
@Dutch.Boyd's answer contradicts the very TDA he posted with it.
Therefor, in a NL game, if you bet 500 and the action comes back to you, you may only re-raise if another player has made a full raise behind you.
A full raise is defined below:
In the example above, the shortstacked player raised to 750, which is not a full-raise, so you may only call or fold.
This is different for Fixed-Limit poker.
However, this is irrelevent since op specified Hold'em No Limit in his question.
I think @Dutch.Boyd was confused because of the top part of rule 41:
This is not talking about all-in rules.
Based on the same example above, it means that if you bet 500 and the next person throws in 700 without announcing "raise", it is actually considered a call instead, because he didn't put in at least 50% of the minimum raise. He must remove the extra 200 chips and cannot make it a raise.
But if he had thrown in 750, it would considered a raise because it's at least 50%. But, he must put in the full raise amount, so it becomes 1000 instead.
Min-Raise (preflop), Bet (flop, turn, river)