NACHA File Format: Examples & Complete Guide

1. What Is a NACHA File?

A NACHA file (sometimes called an ACH file) is a standardized flat-text file used to instruct banks to process electronic payments through the Automated Clearing House (ACH) network. NACHA stands for the National Automated Clearing House Association, the organization that defines and maintains the file format specification.

Every line in a NACHA file is exactly 94 characters long. The file uses a fixed-width format — meaning each field occupies a predefined number of character positions, padded with spaces or zeros as needed. Files typically carry the .ach extension and are uploaded to your bank's ACH portal to initiate payments or collections.

Because the format is strict and unforgiving, even a single character out of place will cause a bank to reject the file. That is why understanding the structure — and using reliable tooling — is essential.

2. NACHA File Structure Overview

A NACHA file is organized in a strict hierarchy. Think of it as a container (the file) holding one or more batches, each of which holds one or more payment entries:

• File Header (1) — Identifies the originating company and destination bank. One per file.
• Batch Header (5) — Groups related entries (e.g., all payroll payments). A file can contain multiple batches.
• Entry Detail (6) — A single payment or collection instruction to/from one account.
• Addenda (7) — Optional additional information attached to an entry (used in certain SEC codes like CTX).
• Batch Control (8) — Summary totals for the preceding batch: entry count, dollar totals, and entry hash.
• File Control (9) — Summary totals for the entire file. Followed by padding lines of all 9s to make the total line count a multiple of 10.

3. File Header Record (Record Type 1)

The File Header is always the first line in a NACHA file. It identifies who is sending the file and where it is going.

4. Batch Header Record (Record Type 5)

Each batch groups related payment entries — for example, all payroll deposits or all vendor payments. A single NACHA file can contain multiple batches with different SEC codes or effective dates.

5. Entry Detail Record (Record Type 6)

Each Entry Detail record represents a single ACH transaction — a credit (deposit) or debit (withdrawal) to a specific bank account. This is where the actual payment amounts and recipient details live.

6. Batch Control Record (Record Type 8)

The Batch Control record closes a batch and contains summary totals used for validation. Banks compare these totals against the individual entries to detect transmission errors.

7. File Control Record (Record Type 9)

The File Control record is the final meaningful record in a NACHA file. It contains aggregate totals across all batches in the file, serving as a final integrity check.

After the File Control record, the file is padded with lines consisting entirely of the digit "9" (94 nines per line) until the total number of lines is a multiple of 10. This is called blocking — the blocking factor is always 10.

8. Complete NACHA File Example

Here is a complete, annotated NACHA file. This example contains one batch with three credit entries (a payroll run paying three employees), padded to a 10-line block:

9. NACHA File Format in Excel

Many businesses first encounter NACHA files when they try to build one in Excel or Google Sheets. While it is technically possible, the approach is fraught with challenges:

• Fixed-width formatting — Every field must be padded to an exact character length. Excel's default CSV export strips leading zeros and trailing spaces, breaking the format immediately.
• Numeric precision — Routing numbers and account numbers with leading zeros are treated as numbers by Excel, which silently drops the zeros (e.g., 021000021 becomes 21000021).
• Hash and total calculations — The Batch Control and File Control records require computed values (entry hash, total debits, total credits, entry counts) that must exactly match the individual entries. A single error means rejection.
• Blocking / padding — The total number of lines must be a multiple of 10, padded with 9-records. This is easy to forget.
• No validation — Excel cannot validate routing number check digits, verify SEC code rules, or enforce NACHA compliance rules.

10. Common NACHA File Errors

When banks reject a NACHA file, it is usually due to one of these issues:

Frequently Asked Questions