The Retainer Invoice is a specialized billing document used in Pakistani business contexts where services are provided on an ongoing basis for a set fee. This document type is essential when a service provider has established a continuing professional relationship with a client and needs to bill regularly for reserved time or services. It must comply with Pakistani tax regulations, including proper documentation of sales tax and income tax. The retainer invoice should be used when there is a pre-arranged agreement for ongoing services, typically including professional services, consulting, or advisory work. It differs from standard invoices by including specific retainer period details, service level commitments, and potentially unused service allowances. The document serves multiple purposes: as a billing instrument, a tax document, and a record of the ongoing professional engagement.

1. Invoice Header: Contains the invoice number, date, and the word 'RETAINER INVOICE' clearly displayed

2. Service Provider Details: Complete business information of the service provider including name, address, contact details, and tax registration numbers

3. Client Details: Complete business information of the client including name, address, and contact details

4. Retainer Period: Clear specification of the billing period covered by the retainer

5. Service Description: Brief description of the services covered under the retainer agreement

6. Fee Details: The retainer amount, clearly stated in both numbers and words

7. Payment Terms: Payment due date and accepted payment methods

8. Tax Details: Breakdown of applicable taxes including income tax and sales tax as per Pakistani law

9. Total Amount: Final payable amount including all taxes and charges

10. Banking Details: Service provider's bank account information for payment