How ACH works
The Automated Clearing House network is the main system of electronic funds transfer in the US. Since the 1970s, it aimed to allow the transfer of predictable and regular payments without the need of paper checks. The main principle of the network was stability, not speed.
An ACH instruction begins as an instruction from an originating bank to a recipient bank. The instruction is sent in the form of a digital file through the Federal Reserve, which acts as the clearinghouse. The recipient bank is required to process their backlog of instructions by 8:30 AM every day, called the settlement window. The ACH uses a pre-email system of electronic file transfer where there is no contact between the two banks. The settlement windows are the only time when the originating financial institution will be informed that the recipient bank has processed the originating bank’s ACH instructions.