How to Invoice as a Marketing Agency
A step-by-step guide to agency invoices: the scope, the retainer, project stages, extra hours, costs you pay for clients and the details their accounts team needs.
In the US, the Bureau of Labor Statistics' Occupational Outlook Handbook (page last modified August 27, 2026) says "Advertising, promotions, and marketing managers plan programs to generate interest in products or services." An agency does that work for clients, and its invoices have to separate three things: the agreed monthly or project fee, any hours beyond it, and costs paid on the client's behalf.
This guide follows an agency invoice in order: the scope, the retainer, project stages, extra hours, costs, purchase orders, then payment and follow-up.
Worked example (sample figures): on a $3,500.00 monthly retainer, the team logs 8 extra design hours in May at $95.00, or $760.00, and buys a $120.00 stock photo license for the client. The retainer goes out on its recurring invoice; the extra hours and the license go on a second May invoice: $760.00 + $120.00 = $880.00, so the client pays $3,500.00 + $880.00 = $4,380.00 for May. Use your own fees and rates; these are only an illustration.
Step-by-step invoicing guide
- 1
Get the scope approved
Write down what the retainer or project includes, how extra hours are charged and which costs the client pays, and send it for approval. Billed's features page says "Yes your clients can approve or reject your estimates online." and "Convert your estimate to invoice with a single click after getting approval from your client." Billed's estimating page says you can "Share your online estimates with your clients via shareable public link."
- 2
Bill the retainer on a schedule
Billed's recurring invoices page says: "Establish a stable cash flow with retainers." Billed's invoice software page says: "For clients you bill on a schedule, set up a recurring profile once." It adds: "Choose the billing frequency (daily, weekly, monthly or yearly) and how many invoices to send, or keep sending until you stop."
- 3
Bill project fees in stages
For a campaign or a website build, split the fee by stage on one invoice. Billed's help article on payment schedules says: "A payment schedule lets you add a payment plan to the invoices." Its steps include: "Fill out the payment amount and due date of each payment." The same article says "the sum of all the payments should be equal to the total balance of the invoice."
- 4
Bill extra hours from tracked time
Track the team's time on the client's project, then bill hours beyond the retainer as their own line. Billed's time tracking page says: "Invite teammates, accountants and contractors to your Billed account and grant them permissions, so the whole team tracks its time in one place." Billed's help article on timesheet invoices says: "Billed allows you to generate invoices against billable time log entries."
- 5
Pass on costs you paid for the client
Stock licenses, printing or freelancer costs that the client agreed to pay go on the next invoice. Billed's help article on creating an invoice says: "If there are any unbilled expenses of a particular client, you can add these expenses to the client's next invoice." and "The expense will appear as a line item in the invoice."
- 6
Add the client's PO and campaign name
Ask the client's accounts team what they need on each invoice, such as a purchase order number or a campaign name, and include it every time. Billed's invoice software page says: "Add files to your invoices and estimates."
- 7
Set payment terms and chase late invoices
Billed's invoice software page says: "Set a due date on each invoice so your client knows when to pay." Billed's help article on payment reminders says: "You can set a schedule of payment reminders before and after the invoice's due date." and "You can send up to three reminders." Billed's mobile app page says: "Invoices carry a pay button when Stripe or PayPal is connected, so clients can pay by card the minute they receive it."
Tips for marketing agency invoicing
- Agree on what the retainer covers each month before the first invoice, and list it in the scope.
- Send a timesheet with any invoice that bills extra hours. Billed's time tracking page says you can "Create timesheets from the time you and your team have tracked to see how the team is spending its time, and export them when a client or your accountant needs a copy."
- Bill costs in the month you pay them, so the client's budget lines up with your invoices.
- Keep one invoice per brand or business unit when each has a budget of its own.
- Number invoices in sequence. Billed's help article on creating an invoice says: "Each new invoice number will be one number greater than the previous invoice number."
Common invoicing mistakes to avoid
- Doing extra work inside the retainer without telling the client it's extra.
- Billing a whole project at the end, after months of work.
- Paying costs for the client and forgetting to put them on the next invoice.
- Leaving off the purchase order number, so the client's accounts team may send the invoice back.
- Combining fees, extra hours and costs into one total the client can't check.
How this works in Billed
Recurring Retainers
Billed's recurring invoices page says: "Establish a stable cash flow with retainers." Billed's invoice software page says: "For clients you bill on a schedule, set up a recurring profile once." It adds: "Choose the billing frequency (daily, weekly, monthly or yearly) and how many invoices to send, or keep sending until you stop."
Team Time Tracking
Billed's time tracking page says: "Invite teammates, accountants and contractors to your Billed account and grant them permissions, so the whole team tracks its time in one place."
Invoices From Billable Time
Billed's help article on timesheet invoices says: "Billed allows you to generate invoices against billable time log entries." Billed's time tracking page says you can "Create timesheets from the time you and your team have tracked to see how the team is spending its time, and export them when a client or your accountant needs a copy."
Costs on the Next Invoice
Billed's help article on creating an invoice says: "If there are any unbilled expenses of a particular client, you can add these expenses to the client's next invoice." and "The expense will appear as a line item in the invoice."
Payment Schedules
Billed's help article on payment schedules says: "A payment schedule lets you add a payment plan to the invoices." Its steps include: "Fill out the payment amount and due date of each payment."
Frequently asked questions
Start Invoicing With Billed
Set up your account and send your first invoice with Billed.
At a glance
- Retainer: the same invoice each month.
- Project: one invoice, split by stage.
- Extra hours: tracked time, billed on its own line.
- Costs bought for the client: billed on a separate invoice from the retainer.
- Client paperwork: the PO number and campaign name on every invoice.
When this isn't for you
This guide covers agencies that invoice clients for their own fees and the costs they pay. If the client pays ad platforms and vendors directly, you only bill your fees.