ACH, Same Day ACH, RTP, FedNow or Cards: Routing Payments by Need
Asking which payment rail is best is a bit like asking which vehicle is best. The answer depends on what you are carrying and how soon it has to arrive. A US business today can choose among batch ACH, Same Day ACH, the instant networks RTP and FedNow, and cards. Each one trades cost, speed and finality differently, and a well-designed product uses more than one of them.
The rails at a glance
| Rail | Timing | Finality | Best suited to |
|---|---|---|---|
| ACH | Batch, on banking days | Can be returned later | Payroll, recurring B2B, low-cost flows |
| Same Day ACH | Three settlement windows per banking day | Can be returned later | Faster batch payments up to $1 million each |
| RTP | Immediate, around the clock | Final | Urgent disbursements |
| FedNow | Immediate, around the clock | Final | Urgent disbursements |
| Cards | Instant authorization | Depends on card network rules | Customer checkout where immediate approval matters |
ACH: the low-cost workhorse
The Automated Clearing House moves more than 30 billion payments a year, under the Nacha Operating Rules, through two operators: the Federal Reserve and The Clearing House. It carries payroll, vendor payments, subscriptions, insurance premiums and rent.
Its strength is low unit cost. Its weakness is that it is asynchronous. A payment accepted for processing can still come back. Most returns arrive within two banking days of settlement, and consumer claims of an unauthorized debit can be returned for up to 60 calendar days after settlement. Any product that uses ACH has to plan for that.
Same Day ACH: faster, still batch
Same Day ACH sits between ordinary batch and instant payments. There are three settlement windows on each banking day, and a limit of $1 million per payment. It suits cases where tomorrow is too late but round-the-clock delivery is unnecessary. Your software needs to understand the windows, the limit and federal banking holidays, or your team will end up tracking them by hand.
Keep in mind that Same Day ACH is still ACH, so returns remain possible.
RTP and FedNow: instant and final
RTP and FedNow provide immediate, final settlement at any hour. That makes them attractive for urgent disbursements and for any case where finality itself has value, since the recipient knows that the money has really arrived.
Finality also cuts the other way. Once funds have moved they are hard to recover, so a fraudulent instant payment gives you very little room to respond. Instant rails need stronger checks before release, because there is no useful "after".
Cards: instant approval, higher price
Cards give an instant authorization at a higher price than bank-based rails. They remain a natural choice where a customer is at the checkout and needs an immediate yes.
Routing by need
A simple way of thinking about routing is to ask three questions of each payment:
- How urgent is it? If it can wait, ACH is hard to beat on cost. If it needs to land today, consider Same Day ACH. If it needs to land now, consider an instant rail.
- How much does finality matter? If certainty is the point, instant rails help. If you might need to correct the payment, finality is a risk you should weigh up.
- What happens if it is fraudulent? The faster and more final the rail, the more of your defense has to happen before the money leaves.
In general, payroll and recurring B2B payments belong on ACH. A time-critical payout may justify an instant rail. A customer buying something right now is often best served by a card.
A note on the fraud rules
On ACH, Nacha's 2026 fraud monitoring rules now cover all non-consumer originators and third parties, after a Phase 2 practical date of June 22, 2026. Covered parties need risk-based processes, reviewed at least annually, to identify entries initiated through fraud and false pretenses. This is a general summary and not legal advice, so please check how it applies to you with your bank.
Building for more than one rail
The most useful design decision is to keep the rail behind an internal interface. Your application should express an intent, such as "pay this supplier by this time", and a routing layer should choose how. With that abstraction in place, adding a new rail later does not force you to rethink your ledger.
Keep your own ledger as the source of truth across all rails, with each one reporting into it. That way, a returned ACH entry and a final instant payment are both recorded honestly in one place. If your routing logic is specific to your business, this is a sensible area for custom software development.
For a closer look at the ACH side, including how to compare products and what to own yourself, see our complete guide to ACH software.
Frequently Asked Questions
What is the main difference between ACH and RTP?
ACH processes payments in batches and allows returns after the fact, while RTP settles immediately with finality at any hour. ACH generally suits low-cost, non-urgent flows, and RTP suits urgent ones.
Can Same Day ACH be used for any amount?
No. Same Day ACH carries a limit of $1 million per payment and operates in three settlement windows on each banking day, so larger or out-of-window payments have to go another way.
Are instant payments riskier than ACH?
They carry a different fraud risk. Since funds settle immediately and are hard to recover, checks must happen before release. ACH offers more time, although it brings the separate complication of late returns.