Duplicate invoices: What they are and how to prevent them

Duplicate invoices—entries that appear more than once in accounts payable—are common even in well-managed finance teams. They can happen when a vendor resends an unpaid invoice, an AP clerk keys one in twice, or in some cases, as part of a fraud attempt.

Unaddressed, duplicate invoices drive up costs, slow approvals, and create reconciliation headaches. They can lead to overpayments, strained vendor relationships, and financial reporting errors.

What are duplicate invoices?

A duplicate invoice is any invoice that appears more than once in a company’s accounts payable system. Some are exact copies, with the same invoice number, vendor, and amount, while others show slight variations, like a different date or formatting change.

Many duplicate invoices result from human error or system glitches, but they can also signal deeper issues such as fraud. Either way, they create unnecessary risk in the AP process.

Some finance teams use “double invoice” interchangeably with “duplicate invoice.” Technically, a duplicate invoice is any repeated entry in your AP system, while a double invoice usually refers to the same bill submitted and paid twice.

Why duplicate invoices are an issue

Duplicate invoices often begin as small mistakes, but the impact adds up quickly:

• Overpayments: Paying the same invoice twice drains cash and requires recovery efforts
• Cash flow disruption: Duplicate payments reduce available working capital until funds are returned
• Reconciliation challenges: Extra entries complicate month-end close and financial reporting
• Audit and compliance exposure: Patterns of duplicate payments can point to weak controls
• Manual rework: Teams spend hours investigating discrepancies and coordinating refunds
• Vendor tension: Overpaying and requesting reimbursement can erode trust

Even if duplicates are eventually caught, they consume time and resources and repeated problems undermine internal credibility and vendor relationships.

Industry research from Celonis found duplicate payment rates typically range from 0.1% to 0.5% of total outgoing payments, and in some cases reach as high as 1.5%. For a company processing $100 million annually, that could mean up to $1.5 million at risk each year.

Common reasons duplicate invoices occur

Duplicate invoices can result from routine errors or deliberate fraud. The challenge is knowing which is which and putting controls in place to catch both.

Non-fraudulent causes

Most duplicates stem from everyday mistakes in manual entry or system processing:

• Manual data entry: An invoice is keyed in twice, often because it wasn’t clear whether it had already been entered
• Vendor resubmissions: When a vendor doesn’t receive payment on time, they may resend the invoice. Without a tracking system, both versions can be processed
• System limitations: AP automation tools may miss near-duplicates if OCR misreads details—for example, reading an “8” as a “B”
• PO corrections: An invoice may be resubmitted with a revised purchase order number while all other fields remain unchanged

These cases are rarely intentional, but they can still cause overpayments, accounting discrepancies, and vendor confusion if not flagged early.

For example, imagine an AP clerk receives the same invoice by email and by mail. Without a centralized intake process, they key it in twice. Unless flagged, the system processes both entries, leading to an unnecessary duplicate payment.

Fraudulent tactics

Intentional duplicates rely on subtle changes or timing to slip past internal checks:

• Slight variations: The same invoice is resubmitted with a minor edit, such as a new date or invoice number, to avoid detection
• Ghost vendors: A fake vendor profile is created to submit false invoices under thresholds that don’t require multiple approvals
• Invoice splitting: A high-value invoice is divided into smaller ones to sidestep higher approval requirements
• Timing attacks: Fraudulent invoices are submitted during high-volume periods, such as month-end close, when oversight is more likely to slip

These tactics succeed because they resemble legitimate transactions while exploiting process gaps.

How to distinguish between error and fraud

It isn’t always clear whether a duplicate invoice is an oversight or intentional fraud. Certain patterns can help you assess intent and decide which cases need closer review.

No single factor confirms intent, but taken together, these signals show which invoices deserve further review.

Best practices for preventing duplicate invoices

Even with advanced tools, preventing duplicate invoices depends on process discipline. These practices reduce both accidental errors and opportunities for accounts payable fraud:

• Centralize invoice intake: Route all invoices, regardless of format, through a single platform or intake team to avoid duplicates from multi-channel submissions
• Standardize formatting: Ask vendors to use consistent invoice numbers, dates, amounts, and PO references. Structured data makes validation easier.
• Enforce validation checks: Confirm invoice details against vendor records, purchase orders, and past payments before issuing payment
• Minimize manual input: Reduce manual entry with accounts payable automation. Fewer touchpoints mean fewer chances for duplication.
• Conduct regular audits: Review invoice activity monthly or quarterly to surface patterns and flag irregularities daily workflows may miss

Together, these steps create multiple layers of protection, helping teams catch errors early and reduce fraud risk before payments are made.

How technology helps prevent duplicate invoices

Modern AP tools do more than speed up payments; they build in controls to identify and prevent duplicate invoices before they become costly. Here’s how businesses use technology to reduce risk at scale:

1. Automated duplicate detection

Most ERP and AP automation systems include rules that detect identical or highly similar invoices before they reach the payment stage.

For example, an invoice labeled “INV-1024” might be flagged if a similar one labeled “INV-1024A” was already paid. These alerts prevent accidental overpayments and create a second checkpoint before funds leave the business.

2. Invoice data extraction and validation

OCR-enabled tools digitize invoice details and match them against purchase orders, vendor records, and past transactions. This reduces manual entry and helps catch discrepancies—such as mismatched POs or repeated invoice numbers—early in the process.

3. Risk scoring with AI and machine learning

AI-powered platforms analyze historical payment behavior and assign risk scores to new invoices. These systems can detect patterns—like duplicate amounts with altered dates or minor vendor name changes—and surface invoices that warrant closer inspection.

4. Approval workflow controls

Modern ERP and AP platforms support layered approval workflows. These workflows prevent invoices from being paid before appropriate review, especially when thresholds are exceeded or duplicate behavior is suspected.

Technology adds multiple checkpoints across the invoice lifecycle, helping teams catch errors early while reducing reliance on manual oversight.

How to resolve duplicate invoices

Even with strong controls, duplicate invoices can still slip through. Taking swift, structured action helps minimize disruption and preserve vendor trust:

• Verify the issue: Confirm whether invoices are exact or near-duplicates by checking dates, invoice numbers, payment records, and supporting documents
• Gather documentation: Collect purchase orders, receipts, vendor communications, and prior payment confirmations to understand the full context
• Log the incident: Record the duplicate in your AP or ERP system for audit purposes. If the cause stems from a system or process gap, flag it for internal review.
• Tag or restrict the vendor: Use platform tags, alerts, or approval rules to prevent the same vendor or invoice number from being processed again without extra checks

How to communicate with vendors and recover funds

If a duplicate payment is made, you’ll want to prioritize duplicate payment recovery. A clear and professional response helps manage the vendor relationship while resolving the issue quickly.

• Reach out promptly: Share a summary of the duplicate along with supporting documentation
• Request repayment: Ask for a refund or credit memo based on your internal policy and vendor terms
• Document the resolution: Record the outcome in your system and update vendor notes or workflows to prevent recurrence

Most vendors cooperate when the issue is handled transparently. A documented resolution process ensures accountability and helps your team avoid repeat incidents.

Stop duplicate invoices before they start

Duplicate invoices don’t just happen—they slip through when AP processes are slow, manual, or disconnected. Ramp helps you reduce that risk by streamlining invoice intake, automating reviews, and keeping everything in sync from the start.

With Ramp, you can:

• Automate invoice processing: Use AI-powered OCR to extract invoice details, apply suggested GL codes, and reduce manual errors for clean, audit-ready records
• Simplify approvals with built-in workflows: Route invoices to the right stakeholders with layered rules, automated reminders, and real-time status tracking
• Sync with your accounting tools: Connect with QuickBooks, Xero, NetSuite, and more to keep records accurate and avoid double entries across systems

By the time a payment goes out, you’ve already caught the mistakes, flagged the duplicates, and finalized everything in one place.

Let’s simplify your AP process. Try Ramp invoice management software or explore a hands-on demo to see it for yourself.