What this checker looks for
| Check | What it catches | Confidence |
|---|---|---|
| Same vendor, same invoice number | Invoice numbers are compared after removing spaces, dashes, prefixes like “INV” and leading zeros, so INV-00123 and 123 match. | High |
| Same invoice number and amount, different vendor record | The same bill entered against two vendor records, a common result of duplicate vendor master data. | High |
| Same vendor, amount and date | Re-keyed invoices with a mistyped invoice number. | High |
| Near-identical invoice number, same vendor and amount | One-character typos and swapped digits, such as 10442 and 10424. | Medium |
| Same vendor and amount within the window | Resubmitted invoices, statements paid as invoices and reminders keyed as new bills. Recurring charges will also show here, so review them. | Review |
Why duplicate invoices get paid
Most duplicates are not identical. A supplier re-sends an invoice by email and post, someone keys “INV-2041” and someone else keys “2041”, or the same supplier exists twice in the vendor master under slightly different names. Simple ERP checks only block exact matches on vendor ID and invoice number, so these slip through.
- Duplicate vendor records for the same supplier (different spelling, address or remit-to).
- Manual invoice entry from PDFs and paper, especially at month end.
- Resubmitted or reminder invoices treated as new bills.
- Multiple channels: an invoice arrives by email, portal and post.
- Credit notes and re-issues that are not matched to the original invoice.
How to prevent duplicate payments
- Clean the vendor master and block new vendors that match an existing tax ID or bank account.
- Normalise invoice numbers at entry and check on vendor + normalised number + amount.
- Run a duplicate check like this one before every payment run, not only at audit time.
- Reconcile supplier statements monthly so unapplied credits and double payments surface quickly.
- Match invoices to purchase orders and receipts (three-way match) for goods and services.
Frequently asked questions
Is my invoice data uploaded anywhere?
No. The file is read and checked inside your browser. Nothing is sent to a server, and the page has no analytics on your data.
What file format do I need?
A CSV or tab-separated export, or rows pasted from Excel. You need vendor, invoice number and amount; invoice date makes the results much better. The columns are detected automatically and you can change them.
How many invoices can I check?
Tens of thousands of rows work in a modern browser. For continuous checks across every payment run, use an AP or reconciliation platform.
Why are recurring payments flagged?
Rent, subscriptions and retainers have the same vendor and amount every month. They appear under “Review” so you can confirm them quickly; widen or narrow the window to suit your data.
I found duplicates that were already paid. What now?
Confirm both payments cleared, then ask the supplier for a refund or a credit against the next invoice, and record the recovery. Check the vendor master for a duplicate record so it doesn't happen again.