How to Send an Invoice to a Client: Professional Email Templates & Etiquette

How to Send an Invoice to a Client: The Professional Guide

Completing a demanding project, committing the final code sprint, or securing final design approval is an exhilarating feeling for independent creators and service firms. But between finishing the work and receiving funds in your bank account lies one crucial step: sending the invoice.

While it might seem like a simple matter of clicking "Send," the manner in which you deliver an invoice directly influences your brand perception, your professional credibility, and how fast your payment is processed.

In this guide, we break down the end-to-end invoice submission process, from file naming and formatting to ready-to-use email templates and polite payment reminders.

1. Preparation: File Format Matters

❌ Never send editable Word (.docx) or Excel (.xlsx) files: Spreadsheet columns easily shift between devices, formulas can be broken accidentally, and editable documents appear casual and unpolished.
✅ The Gold Standard: PDF: A portable document format (PDF) guarantees that fonts, alignments, totals, and signatures render identically on any desktop, tablet, or smartphone.

2. Professional File Naming Conventions

Avoid sending files named Invoice1.pdf or Final_Invoice.pdf. Accounts payable departments receive hundreds of attachments weekly. If your file is poorly named, it risks getting lost or delayed in administrative sorting.

Poor: invoice.pdf, doc123.pdf, new-invoice.pdf
Professional: INV-2026-004_AcmeCorp_Q2-Design.pdf or PI-2026-012_ApexAgency.pdf

A standardized filename signals organizational competence and makes it effortless for controllers to file the document against their internal purchase orders.

3. High-Converting Email Templates

Never send an email with an attachment and an empty body. Include an informative subject line and a courteous note summarizing the invoice.

Subject Line Best Practices

Make the subject clear, descriptive, and reference-tagged:

Subject: Invoice INV-2026-004 — Brand Identity Project [Acme Corp]
Subject: Proforma Invoice PI-089 for Sprint 2 Development — [Your Company]

Professional Email Template (Standard Project Delivery)

Subject: Invoice [Invoice-Number] for [Project Name]

Dear [Client Name],

I hope you are having a productive week!

Following our successful milestone review for [Project Name], I have attached invoice [Invoice-Number] for your review.

Invoice Summary:

Invoice Number: [Invoice-Number]

Amount Due: [$X,XXX.00]

Due Date: [Date / e.g. Net 15 days]

Payment Method: International Wire Transfer (Banking details are listed at the bottom of the attached PDF).

If you require any additional vendor forms, W-8BEN/W-9 documentation, or internal PO numbers added to this invoice, please let me know.

Thank you once again for the partnership—it has been a pleasure collaborating on this project.

Best regards,
[Your Name]
[Your Title / Agency Name]
[Phone Number | Website]

4. Strategic Timing: When Should You Send the Invoice?

Immediately Upon Delivery Approval: Transmit your invoice within 24 hours of client sign-off while enthusiasm and appreciation for your work are at their peak.
Optimal Send Times: Avoid late Friday afternoons or chaotic Monday mornings when inboxes are overflowing. Tuesday, Wednesday, and Thursday mornings typically yield the highest open rates and faster approvals.

5. Polite Payment Follow-Up Cadence

If an invoice is approaching its due date or has become overdue, send a structured sequence of gentle reminders:

2 Days Before Due Date:

"Hi [Name], quick friendly reminder that invoice [Number] for [$X,XXX] is due in two days on [Date]. Please let me know if your finance team needs any supplementary details to process the transfer."
1 Day Past Due Date:

"Hi [Name], I wanted to follow up on invoice [Number], which was due yesterday. Could you please confirm if this has been submitted for payment scheduling?"
7 Days Past Due Date:

"Dear [Name], our accounting records show that invoice [Number] ($X,XXX) is now one week overdue. Please review and provide an estimated date of disbursement so we can update our receivables ledger."

6. Automate Your Invoicing with Proformam

Managing templates, calculating VAT, and formatting PDF files manually can consume hours every month. With Proformam, you can:

Create pristine, multi-currency PDF invoices in under a minute.
Send invoices directly to your client's inbox via a formatted email notification.
Store and archive past billing records in a secure cloud dashboard.

Create your next invoice in seconds with our free online invoice generator.