Technology to support Hybrid Automatic Retransmission re-Quest (HARQ) for Carrier Aggregation (CA) is disclosed. For example, a device, at a processor residing on a User Equipment (UE), includes a sizing module and a window module. The sizing module can be configured to determine a first size of a first bundling window for a first Component Carrier (CC) and a second size of a second bundling window for a second CC. The window module can be configured to: generate a first virtual window comprising a selected number of DownLink (DL) sub-frames in the first bundling window that are added to DL sub-frames in the second bundling window; and generate a second virtual window comprising remaining DL sub-frames from the first bundling window that are not added to the first virtual window. The selected number of DL sub-frames can be proportional to a difference between the first size and the second size.