If you are evaluating instant payments in the US, you will run into three rails fast: The Clearing House RTP network, the Federal Reserve's FedNow Service, and plain old ACH.
Here is the quick answer: RTP and FedNow can move funds in seconds, 24/7, and settle right away, but they are push-only and require your bank or payments partner to support the rail. ACH is slower and batch-based, but it is widely supported, familiar for vendor payments and payroll, and still cost-effective when you do not need instant settlement.
This guide explains how each rail works, what "final" means in practice, and how to choose the right one for merchant payouts, supplier payments, and pay-by-bank checkout.
RTP and FedNow are instant account-to-account payment rails that clear and settle individual payments immediately, while ACH is a batch-based network that processes files in scheduled windows.
RTP is operated by The Clearing House and is designed for bank-to-bank instant payments with immediate clearing and settlement. The RTP network also supports high-value business use cases, and The Clearing House has stated the RTP transaction limit is $10 million. The Clearing House
FedNow is operated by the Federal Reserve and is another instant payment option that participating financial institutions can use to offer instant transfers to their customers. The Federal Reserve frames the service around real-world instant payment impact and use cases through its FedNow Industry Stories content. Federal Reserve Financial Services
ACH is the Automated Clearing House network used for direct deposit, bill pay, B2B payments, and many bank-to-bank transfers. It typically works by originating entries in a batch and settling on a schedule set by ACH operators and banks.
RTP and FedNow settle within seconds when the payment is successfully sent, while ACH settlement is usually next-day or later depending on the type of entry and bank processing windows.
For RTP, "instant" is not marketing language. The Clearing House describes RTP as enabling institutions to move significant sums "in an instant" with immediate clearing and settlement. The Clearing House
For ACH, speed depends on whether you are using standard ACH, next-day options, or same-day options, and on how your bank or provider submits files. Even when you are "faster," you are still in a batch world.
For merchants taking bank payments via a PSP, you should also separate "customer paid" from "merchant has funds available." For example, Stripe notes ACH Direct Debit is a delayed notification method and that a payment typically takes 4 business days to arrive in your account. Stripe Docs
Instant settlement does not always mean "no disputes," but RTP and FedNow payments are generally push payments that are harder to reverse than debit-pull methods.
The merchant takeaway is simple: If you are replacing card payments with pay-by-bank, you need to model reversibility and customer support burden, not just speed and cost.
With ACH Direct Debit, dispute and return rights can be meaningful. Stripe states that customers can generally dispute an ACH Direct Debit payment through their bank for up to 60 calendar days after a debit on a personal account, or up to 2 business days for a business account. Stripe Docs
That does not mean RTP and FedNow are "risk-free." It means the dispute path looks different, and your controls should shift toward payee confirmation, account validation, and payout governance.
For ecommerce checkout, ACH debit and bank transfer products are common today, while RTP and FedNow are emerging as an "instant" pay-by-bank option where supported.
If your goal is lower fees than cards, ACH debit can work well, but you must design for delayed confirmation and returns. Stripe highlights that ACH Direct Debit can take up to four business days to receive notification of success or failure after you initiate a debit. Stripe Docs
If your goal is instant release of goods or instant account funding, RTP or FedNow can be a better fit, but only if your bank, gateway, or pay-by-bank partner can originate and receive on that rail and give you a clean reconciliation experience.
A practical approach for many merchants is to offer two bank options:
For vendor payments and B2B invoices, ACH credit is still the default, while RTP and FedNow can be a strong option for urgent, high-value, or exception payments.
RTP has been used for higher-value, time-sensitive corporate treasury use cases. The Clearing House lists examples like cash concentration and large payments to suppliers or vendors. The Clearing House
ACH credit is still attractive because it is widely supported and tends to be low-cost, and because your AP team and vendors already understand it.
Use RTP or FedNow for B2B when:
Use ACH credit when:
The rail economics usually favor ACH for routine payments, while instant payments can make sense when speed reduces operational cost or prevents revenue loss.
Most merchants do not buy "RTP" or "FedNow" directly. You get these capabilities through your bank, treasury provider, ERP payments module, or a pay-by-bank partner. Pricing varies by provider, and some banks bundle instant payments into treasury packages.
A useful way to think about cost is total cost per payment, not the network fee.
If you are comparing this to card acceptance, do not forget that card costs include interchange, assessment, and processor markup. See our breakdown of how interchange works and why it matters.
Internal link: https://merchantalternatives.com/interchange-fees-explained/
The hardest part is not the rail. It is implementation, reconciliation, and fraud controls.
Here are the issues that tend to surprise teams:
1) Bank and partner availability
RTP and FedNow require that your financial institution participates and that your provider can originate and receive messages for your use case.
2) Reconciliation and remittance data
B2B teams care about what sits next to the dollars: invoice numbers, reason codes, and structured remittance. Make sure your provider can pass remittance details through your ERP or AR system.
3) Exception handling
Your support team will still get "where is my money" tickets. Instant rails reduce timing uncertainty, but you still need clear proof of payment, timestamps, and a way to handle wrong-payee situations.
4) Fraud and internal controls
Instant payments reduce the time window to detect mistakes. That is good when you trust the payee, and dangerous when your approval workflows are weak.
If you have ever dealt with processor reserves and cash flow holds, you already know how painful surprises are. Instant payments can help with cash flow predictability, but only when you implement controls.
Internal link: https://merchantalternatives.com/merchant-account-reserves-and-holds/
ACH is still the right rail when you need broad coverage, predictable workflows, and low cost, and when you can tolerate settlement that is not immediate.
For many merchants, ACH is the "default" for:
Even in a world with instant rails, ACH is not going away because it is integrated into so many business processes.
Ask specific questions about capability, controls, and support, not just "do you support RTP."
Use this checklist:
RTP and FedNow are both instant rails, so the key differences are often about reach through your provider, messaging features, and operational fit.
| Factor | ACH | RTP | FedNow |
|---|---|---|---|
| Settlement speed | Batch-based, not immediate | Immediate clearing and settlement | Instant payments via FedNow participants |
| Availability | Depends on bank windows | 24/7/365 | 24/7/365 (via participating institutions) |
| Typical merchant uses | Payroll, vendor pay, bank debit checkout | High-value supplier pay, urgent B2B | Similar use cases where supported |
| Reversibility | Returns and disputes exist for debits | Push payments, different reversal path | Push payments, different reversal path |
| Implementation | Widely supported | Depends on bank/partner | Depends on bank/partner |
Usually not directly. Most merchants access RTP through a pay-by-bank partner, a bank portal, or a treasury or ERP integration.
No. Both are instant payment rails, but they are operated by different entities and your bank may support one, both, or neither.
Often yes on a pure transaction fee basis, but instant payments can be cheaper overall when speed reduces operational cost or prevents delays.
ACH is not a card chargeback, but debits can be disputed and returned. Stripe notes consumers can generally dispute an ACH Direct Debit for up to 60 calendar days after a debit on a personal account. Stripe Docs
The Clearing House states the RTP network has a $10 million transaction limit. The Clearing House
You can apply for a merchant account through Easy Pay Direct or another processor that fits your model. Other options worth a look: