What Is ACH (Automated Clearing House)
ACH is the US batch-processing network that moves money between bank accounts, payroll, vendor payments, tax transfers, and direct debits, all run through it. Governed by Nacha and operated by the Federal Reserve and The Clearing House, it processes transactions in scheduled cycles rather than continuously, which is why settlement typically takes one to three business days. It is the backbone of domestic US payments, but it was built for predictability, not speed.
How It Works in Practice
Consider a US company paying a supplier in Mexico. The treasury team initiates an ACH credit on Monday morning. The originating bank batches that transaction with others and submits them to the ACH operator by the end of the day. The operator sorts it, routes it to the receiving bank, and net settlement between institutions happens overnight, or potentially the following night, depending on cutoff times and whether the receiving bank has same-day ACH enabled.
For a B2B payment crossing into a foreign bank account, the ACH leg handles the domestic dollar movement, but the transfer then hits a correspondent banking chain before reaching the counterparty. At each handoff, settlement resets. A payment that "left" on Monday may not be available to the recipient until Wednesday or Thursday, and that's under normal conditions, without bank holidays or return requests in the way.
Same-Day ACH narrows this to hours for eligible transactions, but it carries a $1 million per-payment cap and still depends on both banks participating in the same-day windows.
ACH Credits vs. ACH Debits
ACH moves money in two directions, and the distinction matters operationally.
An ACH credit is a push payment; the sender initiates it and pushes money to the recipient. Payroll direct deposit is the classic example. The employer controls the timing, the amount, and the destination.
An ACH debit is a pull payment: the recipient initiates it and pulls money from the payer's account, with prior authorisation. Utility autopay works this way. The company charges you; you've already agreed to let them.
The risk profiles differ. With ACH debits, the payer can dispute or reverse a transaction if it was unauthorised or incorrect; consumers have up to 60 days under Regulation E. Businesses have tighter windows. This return risk is something any finance team processing high volumes of ACH debits needs to account for, because returned payments create reconciliation work and sometimes cash flow gaps.
Why It Matters for Stablecoin Payments
ACH settlement latency isn't just an inconvenience, for treasury teams managing cross-border payables, it creates float, forecasting uncertainty, and FX exposure during the window between initiation and finality. Stablecoin payments on programmable rails settle in seconds, not business days, and finality is on-chain rather than dependent on bilateral interbank net settlement. That removes the 1-3 day window entirely, which matters most when payment timing affects working capital, vendor relationships, or FX hedging decisions.
Merge Context
Merge handles outbound stablecoin payments that bypass ACH settlement windows for cross-border B2B flows, with transaction finality confirmed on-chain rather than through a clearing cycle. For companies reconciling stablecoin receipts against ACH-originated payables in the same treasury ledger, Merge Reconcile maps both rails into a single view, so your team isn't managing two separate settlement timelines manually.
FAQ
Can ACH payments be reversed after they're sent?
Yes, and this is a meaningful operational risk. ACH debits can be returned by the receiving bank for reasons including insufficient funds, closed accounts, or unauthorised transaction claims, in some cases up to 60 days after the original transaction for consumers. For B2B payments, the return window is shorter, but the exposure is real. Stablecoin transfers, by contrast, are final once confirmed on-chain with no network-level reversal mechanism.
What's the practical difference between Same-Day ACH and real-time rails like RTP or FedNow?
Same-Day ACH still processes in batches, it just runs more of them per day, with the last cutoff at 4:45 p.m. ET. RTP and FedNow move money in seconds, 24/7/365, with immediate interbank settlement. The distinction matters for treasury operations that need certainty of receipt outside banking hours or at amounts above Same-Day ACH's $1 million limit.
Why do some stablecoin payment providers still reference ACH in their infrastructure?
Many stablecoin platforms use ACH for the fiat on-ramp and off-ramp legs, converting dollars in or out of a bank account before or after the stablecoin transfer itself. The stablecoin movement between wallets is instant; the ACH leg is what introduces latency at the edges. Merge is designed to minimise reliance on ACH in the payment flow by keeping as much of the transaction on-chain as the counterparty's setup allows.
