How to write an invoice email (subject lines and templates)
A complete guide to writing an invoice email, with subject line formulas, ready-to-use templates, and what to include so clients pay faster.
Most of the invoice itself is fixed — the line items, the total, the due date. The email it's attached to is the part you actually get to write, and it matters more than people think. A vague subject line gets filed under "later." A clear one, with the right information right there in the email body, gets opened, understood and often paid the same day. None of this needs to be clever. It just needs to be consistent.
Why the email matters as much as the invoice
A client who's busy doesn't read invoices closely the first time — they skim the email to work out three things: who this is from, how much they owe, and by when. If those three things aren't obvious in the first few seconds, the email gets pushed down the inbox and the invoice sits there unopened, or opened and forgotten. Writing a good invoice email isn't about sounding formal. It's about making those three facts impossible to miss.
Subject lines that actually get opened
A subject line has one job: tell the reader exactly what this email is before they open it. Avoid anything generic like "Invoice" or "Following up" — in a busy inbox, those get skimmed past. A good formula includes your business name, the word "invoice," and either the invoice number or the amount:
- "Invoice #1042 from [Your Business] — $480 due 14 Oct"
- "[Your Business]: Invoice for October design work ($1,200)"
- "Reminder: Invoice #1042 ($480) due today"
If you invoice the same client regularly, keeping the format identical every time helps too — they'll learn to recognise it and know exactly what to do with it without reading closely.
What belongs in the email body
The invoice attachment (or link) carries the full detail — line items, your business details, payment terms. The email itself should be short and should answer the same three questions the subject line hints at, just slightly expanded:
- What it's for — a one-line description of the work or period covered.
- How much, and by when — stated plainly, not just left for them to find in the attachment.
- How to pay — a link if you take online payments, or your bank details if that's how you're usually paid.
Anything beyond that — a long explanation, a recap of the whole project, extra pleasantries — just adds friction between the client and the action you want them to take.
Template: sending a new invoice
Subject: Invoice #1042 from [Your Business] — $480 due 14 Oct
Hi [Name],
Please find attached invoice #1042 for [brief description of work], totalling $480, due 14 October.
You can pay online here: [payment link]
Or by bank transfer to the details on the invoice.
Thanks for your business — let me know if you have any questions.
[Your name]
Short, specific and easy to act on. There's no apology for sending an invoice and no unnecessary padding — just the facts the client needs to pay.
Template: invoice for a new client
A first invoice to someone you haven't billed before can carry one extra line of context, since they may not yet know exactly how you invoice:
Subject: Invoice #1043 from [Your Business] — $900 due 21 Oct
Hi [Name],
Great working with you on [project]. Attached is invoice #1043 for $900, due 21 October — payment terms and details are on the invoice itself.
You can pay by card here: [payment link], or by bank transfer using the details on the invoice.
Happy to answer any questions about the breakdown.
[Your name]
Template: a friendly reminder before the due date
Sent two or three days before an invoice is due, this one just keeps the date visible without implying anything's gone wrong:
Subject: Reminder: Invoice #1042 ($480) due 14 Oct
Hi [Name],
Just a quick reminder that invoice #1042 for $480 is due this Friday, 14 October.
Payment link: [payment link]
Thanks!
[Your name]
Template: the invoice is now overdue
Once a due date passes, the tone can stay friendly but should name the fact plainly rather than talk around it:
Subject: Invoice #1042 ($480) is now overdue
Hi [Name],
Invoice #1042 for $480 was due on 14 October and I haven't received payment yet. Could you let me know when it's likely to go through?
Payment link: [payment link]
Thanks for sorting this out.
[Your name]
If a client misses this one too, how to politely chase an unpaid invoice has a fuller sequence of follow-ups, including what to do if the silence continues.
A few small things that make a real difference
- Send from a consistent address, ideally one with your business name in it, so clients recognise it at a glance rather than wondering who it's from.
- Attach the invoice as a PDF as well as linking to it if your software supports that — some finance departments only process attachments, not links.
- State the currency explicitly if you ever bill international clients, even when it seems obvious from context.
- Keep a record of what was sent and when — if a client claims they "never got it," having the exact send date and template on file resolves the question in seconds.
- Don't bury the amount or due date in a paragraph. Put them on their own line, or bold, so they can be read without reading the email properly.
Mention your tax or legal position only where it's true
If you're GST- or VAT-registered, that needs to appear on the invoice itself, not just the email — the exact wording and requirements vary by country, so check with your accountant if you're ever unsure what has to be shown. The email doesn't need to repeat tax details; its job is just to get the invoice opened and the payment started.
Making this automatic
Once you've settled on a subject line format and a couple of templates, the time-consuming part isn't writing the email — it's remembering to send it, and then remembering to follow up if nothing happens. InvoiceCharlie sends the invoice email automatically when you issue an invoice, with a payment link built in, and handles the reminder and overdue follow-ups on a schedule so you're not manually tracking due dates across every client.
For the invoice itself rather than the email around it, how to write an invoice covers everything it legally needs to include. And if you need to send a one-off invoice right now without setting anything up, the free invoice generator will build one in a couple of minutes.