The initial call in No Limit poker must be at least as big as the big blind. For example, if you are playing in a No Limit game and the small blind is $5 and the big blind is $10 then you must call at least $10 to call the big blind. If you don't have enough chips to cover the big blind ($10 in our example) then you are eligible only to win the chips that you have matched in the pot.

In order to raise in No Limit the amount of chips that you wish to raise by must be at least as large as the last raise in the same round. In our $5-10 game that means if you are the first to enter the pot in order to raise you must put in $20. Since the big blind is $10 and you wish to raise then you must put in at least $20 (The $10 big blind is considered the raise that you must match).

If someone has already raised before you then your raise must be at least as large as his/her raise. This is not to be confused with the need to match the last bet with your raise. For example, if the blinds are $5-10 and player A sends in a bet of $50 he is raising by $40. If player B wishes to raise he/she must raise by at least $40 (total bet of $90). Many players and even dealers make the mistake of thinking that player B must raise by $50 (total bet of $100) thinking that player B must match the last bet. This is incorrect as the player need only match the raise ($40 in our example).

Now let us consider when a player has gone all in with a partial raise. Other players may not reraise on a player's all in raise unless (a) it is a full raise or (b) they have not yet acted since the most recent full bet or raise. This is complicated so let's use an example.

Suppose we have players A, B, and C in a game where the blinds are $5-10. Player A opens with a raise to $50 total chips (he matches the $10 blinds and raises by $40). Player B reraises all in for a total of $70 total chips (he calls the bet of $50 plus raises $20 more). Player C cold calls the $70. Player A can not reraise since Player B did not put in a legal raise. Player B raised by only $20 when he needed to match a raise of $40. Note that Player C could have raised if he desired, since he had not yet acted in response to the original bet.

Now let us consider an example of when player A could reraise. Again we have players A, B, and C with the blinds at $5-10. Player A raises to a total of $40 chips (he matches the blind of $10 and raises by $30). Player B pushes all in with $70 (calls the $40 and raises by $30). Player C then cold calls. Player A can reraise as much as he wants because Player B has made a legal raise. Player B has matched the original raise amount of $30.