Learn essential invoicing terms including net payment terms, VAT, GST, reverse charge, tax invoices, and credit notes to reduce errors and improve compliance.
Invoicing errors often occur when businesses misunderstand basic terminology. Misusing terms such as Net 30, reverse charge, or tax invoice can lead to delayed payments, inaccurate tax reporting, or compliance issues.
This guide explains essential invoicing terms with clear definitions and references to official tax authorities where applicable.
1. Invoice
An invoice is a document issued by a seller requesting payment for goods or services supplied. Many jurisdictions require invoices to include specific information to support tax reporting and recordkeeping.
2. Invoice Number
A unique, sequential identifier assigned to each invoice. Sequential numbering supports audit traceability and helps prevent duplicate or missing records.
3. Net Payment Terms (Net 15, Net 30, Net 60)
Net payment terms define how many days the customer has to pay after the invoice date (see our detailed comparison of Net 15 vs Net 30 payment terms).
| Invoice Date | Payment Term | Due Date |
|---|---|---|
| April 1 | Net 30 | May 1 |
Clear payment terms reduce disputes and improve cash flow predictability.
4. Due Date
The final date by which payment must be made. Some jurisdictions apply statutory late payment rules if payment is delayed.
5. VAT (Value Added Tax)
VAT is a consumption tax applied in the UK and EU. VAT-registered businesses must generally display:
- VAT registration number
- Applicable VAT rate
- VAT amount charged
6. GST (Goods and Services Tax)
GST functions similarly to VAT in countries such as Australia and Canada. Registered businesses must include required tax details on tax invoices according to national rules.
7. Sales Tax
Sales tax in the United States is typically applied at the state level and generally charged at the final sale. Requirements vary by state.
8. Reverse Charge
Reverse charge shifts VAT responsibility from the supplier to the customer in certain cross-border B2B transactions. Under reverse charge:
- The supplier does not charge VAT
- The customer accounts for VAT
This mechanism applies only in specific legal circumstances.
9. Pro Forma Invoice
A pro forma invoice is a preliminary document issued before goods or services are supplied. It:
- Is not a tax invoice
- Is not used for accounting entries
- Is commonly used for customs or approval purposes
It should clearly state Pro Forma to avoid confusion.
10. Tax Invoice
A tax invoice enables a registered buyer to reclaim VAT or GST where applicable. It must include legally required tax registration details.
11. Credit Note
A credit note reduces or cancels part of an issued invoice. It is commonly used when:
- Goods are returned
- Services were overbilled
- Post-issuance discounts apply
Credit notes must reference the original invoice number.
12. Debit Note
A debit note increases the amount owed, typically due to additional services or billing corrections.
13. Purchase Order (PO)
A purchase order is issued by the buyer before goods or services are delivered. Invoices often reference the PO number for procurement alignment.
14. Remittance Advice
Remittance advice is sent by the customer confirming payment and listing the invoices covered. It supports reconciliation of accounts receivable.
15. Outstanding Balance
The remaining unpaid amount on an invoice. Accurate tracking supports financial reporting, cash flow forecasting, and monitoring your net credit sales.
Common Terminology Mistakes
- Confusing pro forma invoices with tax invoices
- Misapplying reverse charge rules
- Skipping sequential invoice numbers (see our guide on how to write an invoice step by step)
- Omitting required tax registration numbers
Why Understanding Invoicing Terms Matters
- Prevents tax reporting errors
- Reduces client disputes
- Supports audit readiness
- Improves payment predictability
Standardize Your Invoicing
Using structured invoice templates with consistent terminology helps maintain compliance across jurisdictions and reduces administrative risk.