A transmitter is provided. The transmitter includes: a Low Density Parity Check (LDPC) encoder which encodes input bits including outer encoded bits to generate an LDPC codeword including the input bits and parity bits to be transmitted to a receiver in a current frame; a puncturer which punctures a part of the parity bits which is not transmitted in the current frame; and an additional parity generator which selects at least a part of the parity bits to generate additional parity bits transmitted to the receiver in a previous frame of the current frame, wherein a number of the additional parity bits is determined based on a number of the outer encoded bits and a number of the parity bits left after the puncturing.