WHMCS Invoice Customization Guide: Professional Billing Documents

Professional invoices build trust and reinforce your brand with every payment. This guide shows you how to customize WHMCS invoices—from basic branding to advanced PDF templates—to create billing documents your clients will respect.

Basic Invoice Settings

Accessing Invoice Configuration

1. Navigate to Setup → General Settings
2. Click the Invoices tab
3. Configure general invoice options

Invoice Number Format

Customize your invoice numbering:

• Sequential: #0001, #0002, #0003...
• Year prefix: 2026-0001, 2026-0002...
• Custom prefix: INV-0001, INVOICE-0001...
• Next invoice number: Set starting point

Invoice Date Settings

• Invoice created: When invoice generates
• Due date: Days from creation (e.g., Net 7, Net 30)
• Payment terms: Text shown on invoice

Company Information

Essential Details

Configure in Setup → General Settings → General:

• Company name (legal business name)
• Address (full business address)
• Phone number
• Email address
• Tax ID / VAT number (if applicable)
• Business registration number

Logo Configuration

• Upload to Setup → General Settings → General
• Recommended size: 250x80 pixels for PDF invoices
• Format: PNG with transparent background
• Ensure logo is print-quality (high resolution)

Invoice PDF Template

Default Template Location

The PDF invoice template is located at:

• templates/pdf/invoice.tpl

Template Customization Options

• Header section: Logo, company info, invoice number
• Client section: Customer billing details
• Line items: Products, descriptions, amounts
• Totals section: Subtotal, tax, discounts, total
• Footer: Payment terms, notes, legal text

Color Scheme Customization

Match your brand colors in the PDF:

• Header background color
• Table header colors
• Text colors
• Border colors
• Accent colors for totals

Invoice Line Items

Item Display Options

• Product/service name
• Description (configurable per product)
• Billing period (start and end dates)
• Quantity
• Unit price
• Line total

Grouping Options

• Group by product category
• Separate services from domains
• Show add-ons under parent product
• Combine similar items

Tax Configuration

Tax Display Options

• Tax inclusive: Prices include tax
• Tax exclusive: Tax added separately
• Multiple tax rates: Show each tax line
• Tax ID display: Show on invoice

Tax Information on Invoice

Include for compliance:

• Tax rate percentage
• Tax name (VAT, GST, Sales Tax)
• Your tax registration number
• Client's tax number (B2B)

Multi-Currency Invoices

Currency Display

• Currency symbol placement
• Decimal separator preferences
• Thousands separator
• Currency code display (USD, EUR, GBP)

Exchange Rate Notes

For non-base currencies, optionally show:

• Base currency equivalent
• Exchange rate used
• Rate effective date

Payment Information

Payment Instructions

Add clear payment instructions:

• Accept credit cards online
• Bank transfer details
• PayPal payment link
• Check mailing address
• Payment deadline

Pay Now Button

• Direct link to client area payment
• Clear call-to-action
• Mobile-friendly payment page

Custom Fields on Invoices

Adding Custom Information

• Purchase order number
• Project reference
• Client account number
• Department/cost center
• Custom notes per invoice

Conditional Display

• Show PO field only if provided
• Display notes only if entered
• Client-specific information

Invoice Notes and Terms

Global Invoice Notes

Set at Setup → General Settings → Invoices:

• Default notes appearing on all invoices
• Payment terms text
• Thank you message
• Return/refund policy reference

Per-Invoice Notes

• Special instructions for specific invoices
• Promotional messages
• Credit applied notices
• Customized payment arrangements

Invoice Email Customization

Email Template

Located at Setup → Email Templates → Invoice Created:

• Personalized greeting
• Invoice summary
• Payment link
• Attached PDF
• Contact information

Email Best Practices

• Clear subject line with invoice number
• Summary of charges in email body
• Prominent payment button
• PDF attachment for records
• Mobile-friendly format

Invoice Status Display

Status Labels

Proforma Invoices

When to Use Proforma

• Quotes requiring payment before service
• International orders requiring advance payment
• Custom work requiring deposits
• Budget approval requirements

Proforma Settings

• Different numbering sequence
• Clear "PROFORMA" label
• Not included in financial reports
• Converts to regular invoice on payment

Credit Notes

Credit Note Display

• Clear "CREDIT NOTE" header
• Reference to original invoice
• Negative amounts displayed properly
• Reason for credit

Legal Compliance

Required Information by Region

• EU: VAT number, company registration
• UK: Company number, VAT details
• US: State sales tax information
• Australia: ABN, GST registration

Record Keeping

• Sequential numbering without gaps
• Immutable invoice records
• Date and time stamps
• Audit trail for changes

Mobile-Friendly Invoices

Considerations

• Readable on mobile devices
• Touch-friendly payment buttons
• Simple layout for small screens
• Fast loading PDF generation

Testing Your Invoices

Pre-Launch Checklist

Common Customization Mistakes

Conclusion

Professional invoices are a touchpoint that reinforces your brand with every billing cycle. Take time to customize your WHMCS invoice templates with proper branding, clear information, and compliant formatting. Your customers will appreciate the professionalism, and you'll benefit from faster payments.