We report guidelines for symmetric threshold voltage (Vth) in double gate (DG) tunnel FinFETs (tFinFETs) with single and dual metal gate electrodes. To realize the symmetric Vth=±0.2V, the work function difference (ΔΦm) of each gate electrode in n- and p-type tFinFETs with a nondoped Si channel must be 1.34 eV, indicating that tuning the effective work functions in the dual metal gates is difficult. By adding Ge in the channel, the work function required in Ge-channel p-tFinFETs can be reduced to 4.46 eV, furthermore, ΔΦm required to realize a symmetric Vth in n- and p-type tFinFETs can be as small as the minimum value of 0.28 e V. This result means that a symmetric Vth is realized in realistic dual metal gate materials by adding Ge. By using our independent DG tFinFETs with a novel source profile, a symmetric Vth can be realized in a single metal gate in a Ge channel.