ACH (Automated Clearing House) is the backbone of US account-to-account payments: payroll, tax refunds, bill pay, and B2B transfers. NACHA (National Automated Clearing House Association) is the rule-making body that governs the ACH network. This guide explains what ACH and NACHA are, how Same Day ACH works, and how ACH fits with open banking and pay-by-bank in the United States.
For a short definition, see our ACH and NACHA glossary entries, or the NACHA regulation page for the full framework. For a comparison with other payment schemes, see our Payment Schemes guide.
What is ACH?
The Automated Clearing House is a batch payment system that moves money between US bank accounts. Employers use ACH for payroll; the government uses it for tax refunds and benefits; consumers use it for bill pay and transfers; businesses use it for vendor payments and direct debit. In 2024 the ACH network processed 33.6 billion payments valued at $86.2 trillion.
ACH transactions are governed by the NACHA Operating Rules. Two operators process ACH: the Federal Reserve (FedACH) and The Clearing House (EPN). Banks and fintechs participate as Originating Depository Financial Institutions (ODFIs) and Receiving Depository Financial Institutions (RDFIs). Standard ACH settles in one to two business days; Same Day ACH allows same-day settlement up to $1 million per payment.
What is NACHA?
NACHA is the National Automated Clearing House Association, a non-profit that writes and maintains the rules for the ACH network. NACHA does not move funds—the Fed and The Clearing House do that—but it sets the standards that all ACH participants must follow: file formats, deadlines, warranties, and compliance. Membership includes financial institutions, processors, and technology providers.
Key NACHA initiatives include Same Day ACH (same-day settlement), account validation (e.g. for WEB debits), and ongoing rule updates. NACHA also runs the "Preferred Partner" program and publishes ACH network statistics. For the full framework and timeline, see our NACHA regulation page.
Same Day ACH
Same Day ACH allows credits and debits to settle on the same calendar day. Phase 1 (credits) went live in September 2016; phase 2 (debits) in March 2017. The per-payment limit was raised to $1 million in March 2021. Submission deadlines apply (e.g. morning and afternoon windows); funds are typically available to the receiver within hours. Same Day ACH is widely used for time-sensitive payroll, B2B payments, and account funding.
ACH and open banking
In the US, many pay-by-bank and account-funding flows use ACH as the payment rail. Data aggregators (e.g. Plaid, MX, Yodlee) connect accounts for data access; when the user initiates a transfer, the money often moves via ACH. NACHA governs how those ACH payments are formatted and settled; it does not govern how account data is shared—that is the domain of the CFPB Section 1033 (Personal Financial Data Rights) rule and standards like FDX.
Frequently asked questions
ACH (Automated Clearing House) is the main batch payment network in the United States. It moves money and data between bank accounts for payroll, tax refunds, bill pay, and B2B payments. ACH is governed by NACHA Operating Rules and processed by the Federal Reserve (FedACH) and The Clearing House (EPN). Standard ACH settles in 1–2 business days; Same Day ACH allows same-day settlement up to $1 million.