Quick answer. A useful invoice email names the project, identifies the invoice, states the amount and exact due date, and explains how to pay. Attach the correct PDF or include your genuine invoice link, then give the customer a way to raise a question.
Check the invoice before writing the email
The email introduces the bill; it cannot fix an unclear bill. Check the customer’s billing name, invoice number, agreed work, deposits already received, balance, currency, and due date first. Our guide to creating a small-business invoice covers the document itself.
Find out who actually processes the payment. Your project contact and the accounts-payable contact may be different people. If the customer needs a purchase-order number, project code, or vendor reference, include it where they have asked you to put it.
Keep a consistent reference between the document and the message. For example, INV-2026-0042 should mean the same invoice in the email subject, PDF, payment page, and your records. See our invoice numbering examples if you do not have a system yet.
Write a subject line the customer can find again
A searchable subject line is more useful than “Payment” or “Please see attached.” Start with the document type and number, then add your business or project name.
- Invoice INV-2026-0042 — [Business name] — [Project]
- [Project] invoice — [Business name] — due [Date]
- Payment reminder: INV-2026-0042 — due [Date]
Keep the invoice reference unchanged during follow-up. If a customer searches their mailbox for the number printed on the invoice, your message should be easy to recognize. Avoid marking a routine first invoice “urgent” simply to get attention.
Template 1: send an invoice after the work
Use this when you are sending the completed invoice for the first time. Replace every bracketed item, including the payment instruction, before sending.
Subject: Invoice [Invoice number] — [Project]
Hi [Customer name],
Thank you for working with [Business name] on [Project or service]. I’ve attached invoice [Invoice number] for [Brief description].
The balance due is [Amount and currency], with payment due on [Month day, year]. You can pay using [The payment method or genuine invoice link shown on the invoice].
Please let me know if you need a purchase-order reference or have a question about any of the items.
Thank you,
[Name]
[Business name]
[Usual contact details]
Choose either “attached” or “linked” to match what you actually send. If a deposit has already been credited, the balance in this message should be the remaining amount, not the original project total.
Template 2: send an invoice for recurring work
For monthly or other recurring services, state the service period. That helps the customer distinguish the new invoice from the previous one.
Subject: [Service period] invoice [Invoice number] — [Business name]
Hi [Customer name],
Here is invoice [Invoice number] for [Service] provided during [Start date–end date]. The balance is [Amount and currency], due [Month day, year].
[Attach the invoice or provide its genuine link.] Payment instructions are included on the invoice.
[Optional: One short explanation of an agreed change in this period.] Please reply if anything needs clarification.
Thank you,
[Name]
Avoid copying last month’s dates or amount without checking them. If there is an agreed change in scope, make it visible on the invoice and keep the customer’s approval with the job records.
Template 3: follow up after the due date
Check your payment records before sending a reminder. A payment that has not been matched to its invoice should not trigger a message saying the customer has not paid.
Subject: Payment reminder — invoice [Invoice number]
Hi [Customer name],
I’m following up on invoice [Invoice number] for [Project]. The remaining balance is [Amount and currency], and the invoice was due on [Month day, year].
I’ve included the invoice again for convenience. Could you confirm its payment status or let me know if anything is holding it up? If you have already sent payment, please share the payment date and reference so I can check our records.
Thank you,
[Name]
Keep disputes and genuine questions out of an automatic reminder cycle. Our guide to tracking unpaid invoices explains a simple status and follow-up routine.
Use a final sending checklist
- Open the actual attachment and check its customer, number, balance, and due date.
- Confirm the recipient address, billing contact, and any required project reference.
- Check that the email and invoice show the same currency and amount.
- Use a meaningful filename, such as
INV-2026-0042-Project.pdf. - Save the sent message and record when the invoice was delivered.
Make genuine payment instructions easy to verify. The FBI’s business email compromise guidance recommends independently verifying changes to account numbers or payment procedures. Do not rely only on a familiar-looking email thread.
Use the invoice due-date calculator to check a calendar date, or start with our invoice worksheet. Agree payment terms with your customer rather than adding a new deadline or fee in a reminder.
Sources & further reading
Official guidance checked October 21, 2026.
Keep the message and the invoice connected.
Explore WP Labs: Invoice for estimates, invoices, customers, and job records, or use the free worksheet for your next document.