> ## Documentation Index
> Fetch the complete documentation index at: https://www.practiceownersguide.com/llms.txt
> Use this file to discover all available pages before exploring further.

# EFT reassociation

> The money and the explanation travel separately — the ACH deposit through the banking system, the 835 through your clearinghouse. Reassociation proves this deposit is that remittance.

The money and the explanation travel separately. The ACH deposit comes through the banking system; the [835](/concepts/what-is-an-835) comes through your clearinghouse. **Reassociation** proves this deposit is that remittance.

## How it's supposed to work

```mermaid theme={null}
flowchart LR
    P[Payer] -->|835 file| CH[Clearinghouse] --> PM[Your PM system]
    P -->|ACH payment| BK[Your bank account]
    PM -. "TRN trace number" .-> M{Match}
    BK -. "same TRN in ACH addenda<br/>+ BPR10 company ID" .-> M
    M --> R[Reconciled payment]
```

The 835's **TRN segment** carries a trace number. The same number rides the ACH payment's addenda record. The 835's **BPR10** carries the payer's originating company ID, matching the ACH entry. The CAQH CORE rules adopted under the ACA require payers to support this linkage (45 C.F.R. § 162.1602; [CAQH CORE](https://www.caqh.org/core/eft-era-operating-rules)).

## Why it breaks anyway

* **Your bank hides the addenda.** Many banks don't surface ACH addenda at all, or only as a treasury upsell. The trace number exists but you can't see it.
* **Timing skew.** The 835 arrives days before or after the money.
* **One-to-many.** Payers batch or split payments across remittances.
* **Paper.** A check plus EOB has no TRN. Matching falls back to amounts, dates, and check numbers. See [Lockboxes](/concepts/lockboxes).
* **Vendors in the middle.** With aggregators (Zelis, ECHO, Optum), the bank descriptor is the vendor's name, not the payer's. "ECHO Health" in your feed can be any of a dozen payers.

## What unreconciled reassociation costs

Three failures go undetected: **missing money** (an 835 posted as paid whose EFT went elsewhere, the classic [post-bank-switch](/guides/switch-banks) injury), **unexplained deposits** (unapplied cash distorting the books), and **silent shortfalls** (PLB recoupments and card fees absorbed without a decision).

## What good looks like

Every payer deposit matched to its remittance and vice versa, weekly or continuously, with a short exception list someone owns. This is rule-based matching that should not be a human's job.

<Note>
  **Lemma aside:** Lemma is the bank account, so it sees the ACH addenda, parses the remittances, and matches them automatically. Only true exceptions surface ([docs](https://docs.getlemma.com)).
</Note>