Size ambiguity and false alarm rate reduction for polar codes. A user equipment (UE) may determine a decoding candidate bit sequence for a polar-encoded codeword having a codeword size based on a decoding hypothesis for control information having a particular bit length of multiple different bit lengths for the codeword size. The UE may calculate an error detection code (EDC) value for a payload portion of the decoding candidate bit sequence using an EDC algorithm, and may initialize an EDC variable state with at least one non-zero bit value. Scrambling or interleaving of bits may also be performed prior to, or after, polar encoding and may depend on the bit length. In examples, information bits may be bit-reversed prior to generating an EDC value. In examples, the encoded bits may include multiple EDC values to assist the UE in performing early termination and to reduce a false alarm rate.