ACH return reason code

R18 return code: Improper Effective Entry Date

The Effective Entry Date is invalid; the ACH Operator returns the entry.

What R18 means

R18 is the return reason code Improper Effective Entry Date. The Effective Entry Date is invalid; the ACH Operator returns the entry.

It is sent by the ACH Operator as a return entry: the original entry goes back to the ODFI with an addenda record carrying R18, and the ODFI passes the return on to the Originator.

Typical causes

The Effective Entry Date in the batch header is not a valid date, or is outside what the ACH Operator accepts.

Return timeframe

Returned by the ACH Operator at its next file delivery after processing.

What the Originator can do next

Fix the Effective Entry Date (batch header positions 70–75, YYMMDD) and send the batch again.

How R18 appears in a NACHA file

A return is the original entry detail record (type 6) sent back with a return transaction code — 21 or 26 for a checking account, 31 or 36 for savings (21 and 31 return a credit, 26 and 36 a debit) — the original amount, and an addenda record of type 99 that carries the reason. The batch keeps the original entry’s SEC code.

Return addenda record (type 99) with R18
Positions	Field	In an R18 return
1	Record Type Code	7 (addenda)
2–3	Addenda Type Code	99 (return)
4–6	Return Reason Code	`R18`
7–21	Original Entry Trace Number	Trace number of the entry being returned
22–27	Date of Death	YYMMDD for R14 and R15; blank otherwise
28–35	Original Receiving DFI Identification	First 8 digits of the original entry’s RDFI routing number
36–79	Addenda Information	Free text from the RDFI
80–94	Trace Number	The return entry’s own trace number

To read a return file record by record, open the file in NACHA Navigator, a free sister site that parses NACHA files in your browser without uploading them.

Look up R18 from code or an AI agent

The code table on this page is the one behind the REST API and the MCP server, so a script or an AI agent gets the same answer as JSON. No key and no account.

REST · GET · no key

curl -s 'https://payopskit.com/api/v1/codes/R18?set=ach-return'

MCP · tools/call · lookup_payment_code

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "lookup_payment_code",
    "arguments": {
      "code": "R18",
      "set": "ach-return"
    }
  }
}

Response (JSON)

{
  "code": "R18",
  "set": "ach-return",
  "found": true,
  "matches": [
    {
      "set": "ach-return",
      "code": "R18",
      "name": "Improper Effective Entry Date",
      "description": "The Effective Entry Date is invalid; the ACH Operator returns the entry.",
      "details": {
        "category": "return",
        "timeframe": "Returned by the ACH Operator at its next file delivery after processing",
        "timeframeKind": "operator",
        "timeframeDays": null,
        "timeframeFrom": null,
        "account": "any",
        "accountNote": null,
        "writtenStatement": false,
        "initiatedBy": "ACH Operator",
        "note": null,
        "effectiveFrom": null,
        "upcomingChange": null,
        "caveat": null
      }
    }
  ]
}

The MCP server is at /mcp (Streamable HTTP, no key); the API and MCP docs show how to connect Claude, Cursor or VS Code.

The deadline for a settlement date: GET /api/v1/ach/return-deadline?settlement_date=2026-11-25&code=R18 or the MCP tool ach_return_deadline.

Source: Nacha Operating Rules, Appendix Four (Return Entries). The code’s title is the Rules’ own; the rest is this site’s plain-language summary. It is informational and not a substitute for the Rules, your ACH Operator’s schedule or your ODFI agreement.