When a vertical SaaS platform starts integrating payment rails, the question "which one should we support?" turns out to be less obvious than it looks. ACH has been around since the 1970s. RTP launched in 2017. FedNow went live in July 2023. Each operates on different settlement infrastructure, with different latency profiles, different cost structures, and — critically — different network reach across the banks and credit unions your SMB customers use. Picking the right combination requires understanding what those differences actually mean in practice.
ACH: The Backbone Rail
The Automated Clearing House network, governed by NACHA's Operating Rules, moves the majority of commercial electronic payments in the United States by volume. Standard ACH settles in one to three business days, meaning a debit initiated on Monday morning typically settles Wednesday or Thursday. Same-Day ACH, introduced in phased rollouts starting in 2016, compresses that to same-business-day settlement with a cutoff window structure: items submitted before 10:45 AM ET settle by 1:00 PM ET; items submitted before 2:45 PM ET settle by 5:00 PM ET. A third window, introduced in 2021, extends Same-Day ACH availability through 4:45 PM ET for same-day settlement.
ACH is ubiquitous. Every financial institution that participates in the US banking system accepts ACH — including community banks and credit unions that may not yet participate in RTP or FedNow. For a home services platform whose contractors bank at a rural Georgia credit union, ACH may be the only electronic rail that reaches them without fallback to a paper check or debit card.
The cost profile for ACH is low: originating platforms typically pay between $0.20 and $0.50 per ACH transaction for standard credits, with Same-Day ACH carrying a slightly higher fee (NACHA has historically set the Same-Day fee at a fraction of a cent per transaction at the network level, though BaaS providers pass through varied markups). Return handling is where ACH costs can spike — a returned item (R01 insufficient funds, R02 closed account, R04 invalid account number) triggers operational work and may carry return fees, and high return rates can trigger NACHA's ODFi-imposed limits or reviews.
Dispute liability under Regulation E applies to consumer ACH transactions: unauthorized ACH debits on a consumer account must be investigated within ten business days of notice, with provisional credit extended within the first five. For platforms serving SMB customers, Reg E applies to the extent any consumer-level accounts are involved in the chain — typically when the platform's SMB customer is also initiating transfers to personal (consumer) bank accounts.
RTP: Real-Time on the TCH Network
The RTP (Real-Time Payments) network is operated by The Clearing House (TCH), a private entity owned by a consortium of large US banks. RTP transactions settle with finality in seconds — typically under ten seconds from initiation to the receiving bank posting the credit. Unlike ACH, RTP is a credit-push-only network: funds can only be sent, not pulled. There is no "debit" instruction on RTP. Settlement is final and irrevocable; there is no return mechanism for RTP transactions analogous to ACH returns.
RTP's real-time finality changes the operational model for certain use cases meaningfully. An HVAC contractor who completes a job at 6 PM on a Friday and requests payment can receive the funds in their account before they leave the customer's driveway — funds that are available immediately for their weekend expenses, not pending until Tuesday. For platforms where the speed of payout is a competitive feature, RTP settlement finality is the capability that makes the product real rather than nominal.
The coverage gap is the key constraint. RTP network participation has grown substantially — TCH reported over 300 participating financial institutions by 2024, covering the majority of US deposit accounts by volume — but that figure skews heavily toward larger banks. Credit unions and community banks have been slower to adopt, which means a non-trivial portion of the SMB customer base on any given vertical SaaS platform may have accounts at institutions not on RTP. A platform that supports only RTP for payouts will need a fallback rail for those customers.
Transaction limits on RTP have increased over time; the current maximum per transaction is $1 million, though individual financial institutions may set lower limits. For most SMB payout use cases, the per-transaction limit is not a binding constraint.
FedNow: The Federal Reserve's Real-Time Rail
FedNow launched in July 2023 as the Federal Reserve's own instant payment infrastructure. It is architecturally similar to RTP — credit-push only, real-time settlement finality, seconds-latency — but operates under the Federal Reserve's regulatory and operational umbrella rather than a private banking consortium. The strategic significance is that every bank and credit union with a Federal Reserve account has a path to FedNow participation, which is a broader potential network reach than TCH's RTP over the long term.
The practical difference today is that FedNow's live participant count, while growing, started from zero in mid-2023 and is building its network. As of late 2024, several hundred financial institutions were live on FedNow — a meaningful number, but still concentrated among institutions that prioritized early adoption. The geographic and institutional coverage patterns differ from RTP: some institutions that are not on RTP are on FedNow, and vice versa.
For platforms serving government-adjacent or government-funded entities — municipal services contractors, home health care agencies receiving Medicaid disbursements — FedNow's Federal Reserve backing may be a relevant procurement consideration. Some state and local government entities have policies that favor Federal Reserve payment infrastructure over private-consortium alternatives.
How to Choose: A Vertical-Specific Framework
We are not saying one rail is always better than the others — the right answer depends almost entirely on your specific vertical's use case and customer banking profile. Here is how we think through the decision:
Start with ACH as the baseline. Every platform that moves money needs ACH coverage. The network reach is universal, the cost structure is well-understood, and the NACHA rule set is mature and documented. Same-Day ACH solves the majority of "next-day payout" use cases at a cost that is generally acceptable to SMB customers.
Add RTP when instant finality changes the product. If your platform's SMB customers need funds immediately — not tomorrow, not in four hours, but now — and a meaningful portion of them bank at RTP-participating institutions, RTP is worth the integration. Fitness platforms disbursing instructor payments after evening classes, field services platforms paying contractors at job completion, beauty platforms settling stylist tips at end of shift: these are RTP-appropriate use cases where instant finality affects user behavior, not just settlement accounting.
Evaluate FedNow for your specific partner bank's capability and your customer base. If your bank partner is live on FedNow and a significant segment of your customers bank at credit unions that have adopted FedNow before RTP, that is a coverage argument for FedNow. If you are building for government-paying verticals, FedNow's Federal Reserve backing may be worth prioritizing.
Plan for rail fallback logic. A platform that supports RTP but not ACH will frustrate a meaningful portion of its customer base. The correct architecture is: attempt RTP (or FedNow) first for instant-eligible transactions; fall back to Same-Day ACH for non-participating institutions; fall back to standard ACH for edge cases. This logic belongs in the BaaS layer, not in every feature team's code.
The Cost Reality for SMB Platforms
At current market pricing, a platform should expect approximately $0.25–0.50 per standard ACH transaction, $0.50–1.00 per Same-Day ACH transaction, and $0.50–2.00 per RTP transaction (BaaS provider pricing varies; these are realistic ranges rather than guarantees). FedNow pricing from participating banks is not yet standardized and is still establishing market norms.
The cost argument sometimes leads platforms to default to standard ACH for everything to minimize transaction fees. This is the wrong optimization: the value of faster payouts to SMB customers is typically far greater than the fee differential, and platforms that offer instant settlement as a feature can often pass through a small convenience fee that covers the rail cost and generates margin. The conversation should be "what rail best matches this use case" rather than "what rail is cheapest."
The three-rail landscape is going to keep evolving. FedNow's network will grow. RTP's per-transaction limit may continue to increase. NACHA's Same-Day ACH windows may expand further. Building your platform's treasury infrastructure on a BaaS layer that maintains current rail integrations — rather than on a direct bank integration you maintain yourself — means you inherit those improvements without re-engineering your stack each time the landscape shifts.