How to Send an Invoice by Email (With Templates)

Your subject line determines whether your invoice email gets opened promptly or languishes in an overflowing inbox. A good subject line is clear, specific, and includes the key information the recipient needs to prioritise it.

Here are proven subject line formulas:

• Standard: "Invoice #[number] from [Your Name/Business] — Due [date]"
• Project-specific: "Invoice #[number] — [Project Name] — [Month Year]"
• Amount included: "Invoice #[number] for £[amount] — Due [date]"
• Brief and direct: "Invoice #[number] — [Your Business Name]"

A few rules for effective invoice subject lines:

1. Always include the invoice number — This makes it easy for the client to search for and reference later.
2. Include your name or business name — Especially important if the client works with multiple suppliers.
3. Add the due date when possible — This creates gentle urgency without being pushy.
4. Keep it under 60 characters — Longer subject lines get truncated on mobile devices, which is where most people first scan their email.

Avoid vague subject lines like "Invoice attached" or "Payment request". These give the recipient no context and are more likely to be deprioritised. The more specific your subject line, the faster it gets processed.

If this is a follow-up for a late payment, change the subject line to make it clear: "Reminder: Invoice #[number] — now overdue". See our guide on chasing late payments for more follow-up templates.

The email body should be short, professional, and make it easy for the client to take action. Here are three templates for different situations.

Template 1: Standard invoice email

Hi [Client Name],

Please find attached invoice #[number] for [brief project description], totalling £[amount].

Payment is due by [date] via bank transfer. My payment details are on the invoice.

If you have any questions, just let me know.

Thanks,
[Your Name]

Template 2: First invoice with a new client

Hi [Client Name],

It was great working with you on [project]. Please find attached invoice #[number] for £[amount].

Payment is due within [X] days by bank transfer — details are included on the invoice. Please use the invoice number as your payment reference.

If you need anything in a different format or have questions about any line items, I'm happy to help.

Thanks,
[Your Name]

Template 3: Recurring/retainer invoice

Hi [Client Name],

Attached is invoice #[number] for [Month] retainer — £[amount].

As usual, payment is due by [date]. Let me know if you need anything.

Best,
[Your Name]

Keep invoice emails concise. The client doesn't need a recap of the entire project — that's what the invoice itself is for. Your email just needs to identify what's attached, how much is owed, and when it's due.

You have two main options for delivering the actual invoice: attach a PDF to the email, or include a link to an online invoice. Each has advantages.

PDF attachment

• Works offline — the client can view, print, and process it without internet access
• Universally compatible — every device and email client can open PDFs
• Creates a permanent record — the client has the file in their email archive
• Preferred by larger companies and accounts departments who download and file invoices

Invoice link

• Allows online payment — if your invoicing tool supports it, clients can pay directly from the link
• Tracks when the client views the invoice — useful for knowing if they've seen it
• Always up to date — if you need to make a correction, you can update the live invoice
• Cleaner email — no attachment to get caught in spam filters or blocked by corporate email policies

The best approach is to do both: attach the PDF and include a link. This covers all scenarios. In your email, say: "I've attached the invoice as a PDF. You can also view and pay it online here."

One important note: some corporate email systems strip attachments or flag emails with attachments as potential security risks. If a client says they didn't receive your invoice, try resending with just the link. Conversely, if a client's IT policy blocks external links, the PDF attachment ensures they can still access it.

Timing affects how quickly you get paid. Research consistently shows that invoices sent promptly get paid faster than those sent days or weeks after the work is done.

Best practice: invoice on the day you complete the work. If you finish a project on Thursday, send the invoice on Thursday — not the following Monday. Every day you delay is a day added to your payment timeline.

In terms of time of day, aim for Tuesday to Thursday, mid-morning (9-11am). Here's why:

• Monday — Clients are catching up on weekend emails. Your invoice may get buried.
• Tuesday to Thursday — The sweet spot. People are settled into their work week and more likely to process admin like invoices.
• Friday — Acceptable, but the invoice may sit unprocessed until Monday.
• Weekends — Avoid if possible. Your email will be part of the Monday morning pile.

For recurring invoices (monthly retainers), send them on the same date each month — typically the 1st or the last working day. Consistency trains the client to expect your invoice and builds it into their payment routine.

If you're invoicing international clients, consider their time zone. An invoice that arrives at 2pm their time is better than one that arrives at 2am.

Whatever day you choose, the golden rule is: don't wait. The correlation between invoice speed and payment speed is one of the strongest patterns in freelance business. Set up your invoicing workflow so you can send an invoice within minutes of completing a project.

Even with a perfectly written invoice and email, some payments arrive late. Having a follow-up sequence ready saves you time and emotional energy when this happens.

Day of due date: If payment hasn't arrived by the end of the due date, send a brief, friendly reminder. "Hi [Name], just a quick note that invoice #[number] for £[amount] was due today. Wanted to check it's been received and is in the queue for payment. Thanks!"

7 days overdue: A slightly more direct follow-up. "Hi [Name], following up on invoice #[number] for £[amount], which was due on [date]. Could you let me know when I can expect payment? Happy to resend the invoice if needed."

14 days overdue: Time to be firm but professional. "Hi [Name], invoice #[number] for £[amount] is now two weeks overdue (due date: [date]). I'd appreciate a quick update on the payment status. Please note that per our agreement, a late payment fee of [X]% may apply to overdue balances."

30+ days overdue: Escalate. Phone the client if possible. Follow up in writing referencing the Late Payment of Commercial Debts (Interest) Act 1998, which entitles you to charge interest at 8% plus the Bank of England base rate. See our full guide on chasing late payments.

Key principles for follow-ups:

• Always stay professional — anger doesn't get invoices paid faster
• Reference specific invoice numbers and amounts
• Make it easy to pay — reattach the invoice or resend the payment link
• Keep a record of every follow-up for potential legal action
• Consider using payment terms that include early payment discounts as a positive incentive