Copy-paste templates for progress billing
https://archon-partners.com/guides/progress-billing-and-retainers/

From Archon & Partners. Replace everything in [square brackets], read each one, and use it from your own accounts. Check your agreement before mentioning interest, suspension or any contract term. This is not legal or tax advice.

=== 1. Retainer request at signing ===
When: With the signed agreement, before work starts.
Subject: [Project]: retainer invoice to start work

Hi [first name],

Thank you for signing the agreement for [project]. Attached is the retainer invoice for [amount], as set out in [section reference].

We hold the retainer for the length of the project and credit it in full on the final invoice. Work starts on [start date] once it is received.

From [month], we will invoice on the [day] of each month for the work completed in each phase, with a table showing the progress behind each amount.

[your name]
[firm name]

=== 2. Monthly progress invoice cover email ===
When: On your fixed billing day each month.
Subject: [Project]: invoice [number] for [month]

Hi [first name],

Attached is invoice [number] for [project], covering work to [date]. The amount this month is [amount], due on [due date].

The table on the invoice shows each phase, the percent complete and what was billed before, so you can see how the amount is calculated. This month we [one line on progress, for example completed design development and started construction documents].

If anything on it needs explaining, reply here or call me on [your number].

[your name]
[firm name]

=== 3. Progress table for the invoice ===
When: Paste into the invoice body or attach it. The calculator above fills it in for you.
Subject: Progress to [date]

Phase | Fee | % complete | Earned to date | Billed before | This invoice
[Schematic design] | [fee] | [%] | [earned] | [billed] | [amount]
[Design development] | [fee] | [%] | [earned] | [billed] | [amount]
[Construction documents] | [fee] | [%] | [earned] | [billed] | [amount]
[Construction administration] | [fee] | [%] | [earned] | [billed] | [amount]
Total | [total fee] | [overall %] | [earned] | [billed] | [amount]

Hourly services this period: [hours and amount, or none]
Reimbursable expenses this period: [amount, receipts attached]
Retainer held: [amount], credited on the final invoice

=== 4. Final invoice with the retainer credit ===
When: With the last invoice on the project.
Subject: [Project]: final invoice [number]

Hi [first name],

Attached is the final invoice for [project]. It bills the remaining [amount] of the fee and credits the retainer of [retainer amount] received on [date], as set out in [section reference]. The balance due is [balance], by [due date].

Thank you for the work together on [project].

[your name]
[firm name]