Backoff algorithms have been introduced to improve network performance by reducing collisions over networks, especially in large ones. The binary exponential back off used in the standard IEEE 802.11 medium access control makes exponential increments to contention window sizes. The large contention window gaps produced can significantly reduce the network performance. Therefore, a new increment behavior is introduced in this paper, in order to avoid transmissions failure. The Results show that shifting the contention window to the right place based on previous transmissions outperforms the binary exponential back off algorithm, the smart adaptive back off algorithm and pessimistic linear exponential back off algorithm, up to 7.1%, 16.5% and 19% respectively in term of data delivery ratio.