How to Send an Invoice by Email: Subject Lines and Templates

Most invoices are sent as a PDF attached to a short email — and most payment delays start right there, with an email that went to the wrong person, buried the invoice number, or forgot the attachment. This guide covers the mechanics: who to send to, what to put in the subject line, how to write the body in under a minute, and how to resend without sounding awkward.

Send it to the right person (usually not your contact)

The person who hired you is rarely the person who pays you. At any company bigger than a handful of people, invoices go through accounts payable. Before your first invoice, ask your contact one question: "Who should I send invoices to, and is there anything you need on them — like a PO number?"

Then, when you send:

• To: the billing address they gave you (often something like accounts@company.com)
• Cc: your project contact, so they can nudge internally if needed
• One invoice per email. Batching three invoices into one message is how one of them gets missed.

For sole traders and individuals, send directly to your contact — but still cc yourself or use a folder so you have a sent-record.

Subject lines that get opened and found

The subject line has two jobs: get opened now, and be findable in three weeks when someone searches their inbox. That means it needs your business name, the word "invoice," and the invoice number. Good formats:

• Invoice INV-0051 from Harper Copy Co — due Oct 1
• Harper Copy Co — Invoice INV-0051 for September content
• Invoice INV-0051 — Acme project — $1,450 due Oct 1

Avoid vague subjects like "Invoice" or "September billing" (unfindable), and avoid anything cute. An invoice email is the one place where boring wins.

Template 1: the initial send

Keep the body short — everything important is on the PDF. State the amount, the due date, and the invoice number in the text so it survives even if the attachment is overlooked.

Subject: Invoice INV-0051 from Harper Copy Co — due Oct 1

Hi Dana,

Please find attached invoice INV-0051 for September's content work — $1,450, due October 1.

Payment details are on the invoice. If you need a PO number added or anything adjusted for your records, just let me know and I'll send a corrected copy.

Thanks! Priya Harper Harper Copy Co

Template 2: the resend / reminder

Send this a few days after the due date passes (or earlier, as a courtesy nudge before it's due). Assume good faith — most late payments are lost emails, not bad clients.

Subject: Re: Invoice INV-0051 from Harper Copy Co — due Oct 1

Hi Dana,

Just a quick nudge on invoice INV-0051 ($1,450), which was due October 1 — I haven't seen the payment come through yet. I've re-attached it in case the original didn't reach the right inbox.

Could you let me know when it's scheduled? Happy to resend to accounts payable directly if that's easier.

Thanks! Priya

Replying on the same thread (rather than starting a new one) keeps the whole history in one place for both of you.

PDF attachment etiquette

• Always attach a PDF, not a Word document or a link to an editable file. PDFs can't be accidentally altered, open everywhere, and are what bookkeeping software expects.
• Name the file properly: 2026-09-INV-0051-HarperCopyCo.pdf beats invoice_final_v2.pdf. Include the number and your business name — the client may be saving invoices from twenty vendors.
• Attach before you write. The classic failure is the follow-up email that says "with the attachment this time."
• Keep it under a few MB. If your logo is a 10 MB image file, compress it before generating the PDF.
• Paste the key facts in the body (amount, number, due date) so the email is useful even in preview.

A worked example

Here's the invoice behind Template 1 — the actual PDF you'd attach.

Generate the PDF, then hit send

The free invoice maker generates a clean, watermark-free PDF right in your browser — no signup needed — so you can go from blank page to attached-and-sent in a few minutes. Before you send, run your invoice past What to Include on an Invoice: The Complete Checklist so the reminder template never has to leave your drafts folder.