do you HAVE to draw one less card if you mulligan? mtg

[Buster]

do you HAVE to draw one less card if you mulliganin magic?

[Twanos]

yes. The rules are clear that if you don't like your hand for any reason you may "mulligan". The means you return the hand you drew to the library and then reshuffle. Then you draw a new starting hand with 1 less card. You may repeat the mulligan process down to 0 cards if you wish.

Here is the actual rule...
103.4. A player who is dissatisfied with his or her initial hand may take a mulligan. First, the starting player declares whether or not he or she will take a mulligan. Then each other player in turn order does the same. Once each player has made a declaration, all players who decided to take mulligans do so at the same time. To take a mulligan, a player shuffles his or her hand back into his or her library, then draws a new hand of one fewer cards than he or she had before. If a player kept his or her hand of cards, those cards become the player’s opening hand, and that player may not take any further mulligans. This process is then repeated until no player takes a mulligan. (Note that if a player’s hand size reaches zero cards, that player must keep that hand.)

[Arix]

However, if you're playing casually, a common house rule is just to allow free mulligans.