Short answer: A duplicate payment is the same vendor bill paid twice. Most ERPs only block a duplicate when the invoice number matches exactly, so bills typed as 102/26/1620 and 102-26-1620 both get paid. In our sample audit, duplicates were worth 0.6% of revenue. On a $10M company, that is about $60,000 sitting with vendors.
Why your ERP lets duplicates through
NetSuite, QuickBooks, Dynamics and SAP can all warn about duplicate invoice numbers, but the check is usually exact. A human typing a bill reads the same number differently from the person who typed it last month:
- Formatting: INV-0045, INV 45 and 0045 are three different strings to a computer.
- Two vendor records: the same supplier set up twice ("Acme Inc" and "ACME, Inc."), so the bill is checked against the wrong history.
- Two channels: the bill arrives by email and by post, and is entered once by AP and once by the plant.
- Statement payments: a vendor statement is paid in full, including a bill that was already paid on its own.
- Credit memos never applied: the vendor issued a credit, but the next payment ignored it.
How much it costs
Every business is different, which is why we never quote an industry average as your number. In our sample audit of a fictional manufacturer, duplicate vendor payments came to 0.6% of revenue. For a company with $10M in revenue, the same rate would be about $60,000, and the money is real cash already paid out, not a theoretical saving.
A five-step check you can run in Excel
- Export 12 months of paid bills: vendor, vendor tax ID, invoice number, invoice date, amount, payment date.
- Normalize the invoice number: remove spaces, slashes, dashes and leading zeros, and make it upper case.
- Match rows with the same vendor (or the same tax ID) and the same normalized number. These are near-certain duplicates.
- Fuzzy match the rest: same vendor, amount within 1%, invoice dates within 30 days. These need a human look.
- Check the vendor master for two records with the same tax ID or bank account. Every pair is a duplicate waiting to happen.
How to get the money back
Send the vendor a short request with both bills and both payments attached, and ask for a refund or a credit against the next payment. Most vendors agree quickly when the evidence is clear. Offsetting against an open bill is usually the fastest route.
How to stop it happening again
- Normalize invoice numbers at entry, and block payment on a normalized match.
- Merge duplicate vendor records, and allow only one vendor per tax ID.
- Pay only bills that passed a 3-way match: purchase order, goods receipt, invoice.
Questions
How common are duplicate payments?
Common enough that recovery-audit firms have built whole businesses on them. The rate depends on your controls: companies with manual entry, many vendors and no 3-way match find the most.
Can we recover duplicates from last year?
Usually yes. Vendors keep records and most will credit a proven duplicate. The older the payment, the harder it gets, so check at least the last 12 months now.
Do we need new software to find them?
No. An export from your ERP and the five steps above find most of them. Prozone runs the same checks, plus fuzzy matching, in 72 hours as part of a free scan.