Systems and methods for determining and utilizing downlink Hybrid Automatic Repeat Request (HARQ) timing when using short Transmit Time Intervals (sTTIs) are disclosed. In some embodiments, a method of operation of a wireless device in a cellular communications network comprises determining a downlink HARQ timing k for transmission of downlink HARQ feedback for a downlink transmission received in a downlink sTTI nDL based on a Time Division Duplexing (TDD) uplink/downlink configuration and transmitting, in an uplink sTTI nDL+k, downlink HARQ feedback for the downlink transmission received in the downlink sTTI nDL. In this manner, downlink HARQ timing is determined and utilized when using sTTIs.