Single-qubit quantum gates with a subcycle operation time are constructed. Each gate is produced by the action of a subcycle electric-field pulse. Such pulse is shorter than a single-cycle duration 𝑇_0, which is the inverse of the transition frequency of the qubit. This is the opposite limit of the resonant driving where multiple cycles of the field are invovled. Analytical expressions for gate operations are derived in terms of the strength, duration and temporal shape of the pulse. Based on these results, we find the required conditions for implementing particular target gates and estimate the corresponding fidelities. For instance, we show that the NOT gate can be implemented by a symmetric unipolar subcycle pulse Ω(𝑡) with the pulse area ∫Ω𝑑t of 𝜋/2. Furthermore, it is demonstrated that the error converges quadratically in the pulse duration. By pushing the operation time to the subcycle limit, we can not only speed up the quantum gates but also reduce the amount of decoherence in order to conduct accurate computation.