ACH, Bacs and SEPA are the domestic bank transfer schemes of the United States, the United Kingdom and the euro area: batch-based rails used to move money between bank accounts at far lower cost than cards.
Why it matters in B2B collections
For B2B invoices these rails matter because card economics break down at size. A percentage fee on a 90,000 invoice is a meaningful cost, while a bank transfer is typically a flat fee measured in pennies. The trade-off is speed and finality: bank rails clear in batches on a schedule, and some can be reversed after settlement, which changes how confidently an invoice can be marked paid.
Settlement is not the same as finality
The most expensive mistake with bank rails is treating settlement as the end of the story. On Bacs Direct Debit, settlement on day three is the midpoint, not the finish: the ARUDD cycle on days four and five reports which collections actually failed. SEPA Direct Debit goes further, giving consumers an eight week unconditional refund right. ACH debits can likewise be returned after the funds appear. An invoice marked paid on settlement day can therefore un-pay itself, and a collections process that does not model that will overstate cash.
Push and pull are different products
A credit transfer is a push: the customer instructs their bank to send money, and you cannot make it happen. A direct debit is a pull: with a mandate in place, you initiate the collection on the due date. For predictable recurring B2B billing, a pull rail removes the largest single cause of lateness, which is that nobody at the customer got round to actioning the payment. Setting up the mandate is the hard part, and it is a commercial negotiation rather than a technical one.
The reference field is the whole problem
These rails carry very little structured remittance data. A payer typically has a short free-text reference field, and what arrives is frequently a purchase order number, a truncated account code, or nothing useful at all. This is why bank transfers, despite being cheap and reliable, generate most of the reconciliation workload in B2B: the money and the explanation of the money travel separately, and rejoining them is manual unless something automates the match.
The three rails compared
| ACH (US) | Bacs (UK) | SEPA (euro area) | |
|---|---|---|---|
| Operator | Nacha network, US banks | Pay.UK | European Payments Council |
| Typical timing | One to three business days, with same-day ACH available | Three working day cycle: submit, process, settle | SCT within one business day; SCT Inst targets ten seconds |
| Instant option | Same-day ACH, and separately the RTP and FedNow networks | Faster Payments, a separate scheme from Bacs | SCT Inst, now mandated across the euro area |
| Reversal risk | Debits can be returned after settlement | Direct Debit unpaids reported via ARUDD on days four and five | SDD carries an eight week no-questions refund right for consumers |
| Cost shape | Flat, low per transaction | Flat, low per transaction | Flat, low per transaction |
ACH / Bacs / SEPA: common questions
What is the difference between ACH, Bacs and SEPA?
How long does a Bacs payment take?
Is SEPA instant now mandatory?
Why do bank transfers create so much reconciliation work?
Go deeper: Payment providers Finero connects to.
How this connects to other terms
- Cash application
Sparse reference data on these rails is what makes cash application hard.
- Tokenisation
Bank rails sidestep card data entirely, reaching low PCI scope by a different route.