## TL;DR

Shared invoices (software used by three departments) must split across cost centers by a defensible basis: headcount, usage, or fixed percentages. Define allocation rules per vendor or category, apply them at coding time, and require the splits to sum to the invoice total. Document the basis so allocations survive audit.

## Steps

1. Define the allocation basis (headcount, usage, fixed %).
   Expected: A defensible rule.
2. Apply the rule to split the invoice amount.
   Expected: Proposed splits.
3. Verify splits sum to the invoice total.
   Expected: Arithmetic integrity.
4. Get approval from affected cost center owners above a threshold.
   Expected: Consent for shared charges.
5. Store the allocation basis with the invoice.
   Expected: Audit documentation.

## When to use

- Shared vendor invoices
- Multi-department spend
- Allocation policy design

## When not to use

- Single cost center invoices
- PO-matched lines
- Intercompany allocations (different rules)

## Compatibility

ERP-agnostic.

## Variant phrasings

### split invoice cost centers

### allocate invoice multiple departments

### shared invoice coding

## Root cause

One invoice, many beneficiaries. Without allocation rules, the cost lands wherever the coder guesses, distorting departmental results.

## Edge cases

- Allocation bases need periodic revalidation (headcount changes)
- Rounding on splits must still sum exactly; adjust the largest line
- Disputed allocations need an owner to decide

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_eL51wX3qkJDaB50d5TQ2eQ