Understand the three Same-Day ACH submission windows: Window 1 closes at 10:30 AM ET (settlement by 1:00 PM ET), Window 2 closes at 2:45 PM ET (settlement by 5:00 PM ET), and Window 3 closes at 4:45 PM ET (settlement by 6:00 PM ET); all times are Eastern
Set the effective entry date (field in the batch header) to the current business day's date when submitting within a valid window; for standard next-day ACH, set it to the next business day
Validate that the effective entry date is a banking day; NACHA defines banking days as non-weekend, non-Federal-Reserve-holiday days — submitting with an effective date on a holiday shifts settlement to the next banking day
Confirm your ODFI or bank API's internal cutoff, which may be earlier than NACHA's published window cutoffs; many banks apply a 30–60 minute buffer before the NACHA deadline
For returns, remember that Same-Day ACH entries can still be returned within the standard return window (2 banking days for most codes); same-day settlement does not shorten the return window
Known gotchas
Same-Day ACH is not available for international ACH transactions (IAT entries); attempting to submit an IAT as same-day will result in rejection
The third Same-Day ACH window (4:45 PM ET cutoff) was added in 2021 and is not supported by all ODFIs; verify your bank supports the third window before relying on it for late-day submissions
Effective entry date determines settlement timing, not submission timestamp; you can submit a file early in the morning with a same-day effective date and it will settle same-day, or submit it with tomorrow's date for next-day ACH
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