ACH: the batch network that pays America

The Automated Clearing House, or ACH, is the electronic network that moves most of the routine payments in the United States. It is the highest volume payment system in the country, and it processes salaries and government benefits, mortgage and utility payments, business to business payments, and person to person transfers. The network is governed by Nacha, which writes the rules all participants must follow, and it is operated by two operators, the Federal Reserve, which runs FedACH, and The Clearing House, which runs the Electronic Payments Network. A bank connects to one or both operators and exchanges files of ACH transactions with other banks through them. The happy flow is a batch flow, and it runs on files, not on single payments. Follow one payroll. An employer with 1,000 employees runs payroll for a total of 2.4 million dollars, to be paid on Friday. On Wednesday the employer sends a file of 1,000 payments to its bank, known as the Originating Depository Financial Institution, or ODFI. The file has a header, batches, entries and control totals, and the number of entries and the total value must match at every step. The ODFI checks the file, validates the authorisations and the account details, and sends it to the ACH operator, which sorts the transactions and delivers them to the receiving banks, known as Receiving Depository Financial Institutions, or RDFIs. The RDFIs credit the employee accounts on the settlement date, Friday. The whole cycle takes one to two business days for a standard ACH payment, and the analyst must make this timing clear, because the customer experience can look fast while settlement is still a day away. The debit and credit entries show why the file matters. On Wednesday the ODFI debits the employer's account for 2.4 million dollars, or holds the funds, and the file is released to the operator. On Friday the operator settles the net positions between the banks, the ODFI's settlement account is debited and each RDFI's settlement account is credited for its share, and each RDFI credits its employees. If the file control totals do not match, the file is rejected before any of this happens, and the employer must correct and resubmit it. A file with a wrong total is not a partial payment; it is no payment at all, which is why payroll teams reconcile the file totals before submission and again after the operator acknowledges the file. Batches and SEC codes tell the network what each payment is. Each batch carries a Standard Entry Class code, known as a SEC code, which tells the receiving bank what kind of payment it is and which rules apply. PPD is used for consumer credits and debits, CCD is used for corporate credits and debits, CTX is used for corporate payments that carry remittance information, WEB is used for consumer payments authorised online, TEL is used for consumer payments authorised by telephone, and IAT is used for international transactions. The file carries the routing number, the account number, the amount, the transaction code and the company name, and the ODFI must validate the SEC code, the authorisation and the account details before the file is sent. A payment with the wrong SEC code is a compliance failure, not a technical one, because the authorisation rules differ by code: a WEB debit needs an online authorisation record, a TEL debit needs a recorded telephone authorisation, and an auditor will ask to see them. Same Day ACH is the faster option inside the batch network. Same Day ACH was introduced in stages since 2016, and it allows payments submitted before defined cutoffs to settle on the same day. The per transaction limit is currently one million dollars, and only certain SEC codes and transaction types are eligible. A payment submitted after the last Same Day window falls back to standard next day settlement, and the product must show the customer which timing applies. Same Day ACH is still a batch system, so it is not instant, and the funds are not final in the same way as a Fedwire or FedNow payment. An analyst who promises a customer that a Same Day ACH payment is instant has made a promise the system cannot keep, and the complaint will arrive the next morning. Returns are a central part of ACH life, and they use standard return reason codes that every analyst must know. If an account is closed, the RDFI returns the transaction with code R02, if funds are not enough, the code is R01, if there is no account with that number, the code is R03, and if a consumer says a debit was not authorised, the code is R10 for a consumer debit or R29 for a corporate debit, while a revoked authorisation is R07 and a stop payment is R08. A duplicate entry is returned with code R24. The Nacha rules set strict timelines for returns, including a sixty day window for a consumer to dispute an unauthorised debit, and the originator must handle each return promptly. A return that is itself wrong can be dishonoured, and the dishonoured return codes in the R61 to R77 range tell the originator why, for example a duplicate return is R67 and an untimely return is R68. A worked example shows how returns behave at scale. The employer pays 1,000 employees 2.4 million dollars on Friday. On Monday the ODFI receives three returns: one R03 for an employee who gave a wrong account number, one R02 for an employee who closed the account after leaving, and one R01 for an employee whose account could not take the credit. The ODFI must report each return to the employer with the code and the employee, the employer must correct the account details or pay the employee by another method, and the payroll totals must be reconciled so the 2.4 million dollars sent matches the amount credited plus the amount returned. At a 0.3 percent return rate the amounts are small, but at a 5 percent return rate the payroll process is broken and the analyst should be investigating the account data quality, not processing the returns one by one. Cut offs and the calendar decide whether a payment arrives on time. The ODFI sets a file submission cutoff, usually in the afternoon, and a file submitted after the cutoff is processed the next business day. The settlement date is a business day, so a payroll file submitted on Wednesday for Friday settlement works, but a file submitted on Thursday for Friday settlement needs Same Day ACH and may not be eligible. Bank holidays and weekends extend the timetable, and the analyst must design for the calendar, not just the cycle: show the settlement date clearly on every screen, warn when a submission is close to the cutoff, and offer Same Day ACH as the alternative when it is available and the payment is eligible. The authorisation rules are the compliance core of ACH, and they differ by SEC code in ways that matter. A consumer debit needs a valid authorisation that the originator must keep and produce if the consumer disputes the debit. A corporate debit needs an agreement between the companies. An international transaction, IAT, needs additional information about the originator and the destination, including the foreign bank details, because it crosses a border. The Nacha rules also set return rate thresholds, and an originator whose unauthorised return rate exceeds the threshold can be fined and can lose the ability to originate. The analyst must build authorisation capture, storage and retrieval into the product, because a debit without a retrievable authorisation is a liability. ACH is cheap, reliable and deeply embedded in American business, and that is the point. A company that pays a thousand employees every two weeks does not need each salary in seconds, it needs the payroll to be accurate, cheap and predictable. The trade off is speed and finality: an ACH credit can be returned, an ACH debit can be disputed, and the funds are not final in the same way as a Fedwire payment. The analyst must make this trade off clear to the business, so nobody promises a customer that an ACH payment is instant or irreversible when it is neither, and must check the authorisation, the SEC code, the Same Day window, the return code handling and the reconciliation of file control totals before sign off. A payroll that is accurate, cheap and on time is a better product than a payroll that is fast and wrong. The analyst checklist for ACH has six items. First, the file format and the control totals, so a file is rejected before submission if the totals do not match. Second, the SEC code and the authorisation for every batch, with the authorisation record retrievable on demand. Third, the Same Day ACH windows and eligibility, with the settlement date shown to the customer before they confirm. Fourth, the return code handling, with each code mapped to an action and a customer message. Fifth, the return rate monitoring, so a rising R10 or R29 rate triggers an investigation before Nacha does. Sixth, the reconciliation of files sent, files acknowledged, settlements and returns, so the operations team can prove at the end of each day that every dollar sent is either credited or returned.