Monthly billing for a one-person agency

This page shows how to run billing for a one-person agency as one fixed monthly routine: every client invoiced at the rate in their written agreement, setup fees collected up front, retainers billed in advance, hourly work billed from logged time, and late payments handled with the same calm steps every time. It is the routine I run myself on the 1st of each month. It is not tax or legal advice; a section near the end covers when to bring in an accountant.

Before you begin

An accounting tool that sends recurring invoices and keeps your books. I use QuickBooks because invoicing, bookkeeping, and tax preparation live in one place. A lighter invoicing tool works if your books live somewhere else.
A written agreement for every client, such as an accepted proposal or engagement email, stating the rate, the billing terms, and the scope.
A roster of active clients that lives somewhere other than your memory.
A time log, if you bill anything by the hour.
A business bank account, separate from your personal one.

Set your billing terms once

Decide the terms once, write them into every proposal, and stop negotiating them client by client.

Work	When to invoice	Due
Setup fee	The day the proposal is accepted, before the build	Net 15
Monthly retainer	The first month at signing, then on the 1st for the month ahead	Net 15
Project or audit	Half at signing, half on delivery	Net 15
Hourly work	On the 1st, for the previous month's logged time	Net 15
Free or traded work	No invoice. Log what the client owes you instead, such as a case study or permission to reference the work, with a due date.	The agreed date

Put the late-payment steps from this page into the agreement as well, so no step is ever a surprise.

Run the routine on the 1st

Once it is set up, the whole routine takes me about 45 minutes.

Walk the roster, not your memory
Go line by line through your list of active clients. Flag any client you hesitate on.
Send every invoice
Retainers go out at the written rate. Recurring invoices can send themselves, but confirm each one went out for the right amount. Hourly work comes from the time log, rounded to the nearest 15 minutes, with the tasks listed.
Price anything unpriced
Every active client needs a written, agreed rate. If one is missing, send the pricing email this week, or record a dated decision that the work is free and why. An unpriced client should not survive two monthly checks.
Reconcile your revenue numbers
The total invoiced in your accounting tool, the monthly revenue on your project or deal board, and your client roster must match. When they disagree, the accounting tool wins, and the others get corrected that day.
Decide on every below-floor retainer
Draft the price increase now, grandfather it with a dated written reason, or plan the exit. See price floors.
Check the paper
Every line of revenue needs an accepted proposal or engagement email on file. Send a confirmation email for any that do not have one.
Chase anything past due
Use the escalation steps below, in order.
Write the one-line profit and loss
Revenue minus expenses (hosting, domains, software subscriptions, usage-based API fees), as one dated line in a running log. The first month you build the expense list; after that it is a five-minute update.
```
[year-month]: revenue [amount], expenses [amount], net [amount]
```

Make every invoice match the written scope

Use the proposal's names and numbers: the tier, the setup fee, the project. A client holding the invoice next to the proposal should see the same words.
Keep the setup fee and the retainer on separate lines, every time.
Out-of-scope work never shows up as a surprise line. Quote it, get a written yes, then bill it.
Rate changes are agreed in writing before the invoice, never introduced on it.

Bill setup up front and retainers in advance

The setup fee pays for the build, so invoice it the day the proposal is accepted, along with the first month of the retainer, and confirm on the kickoff call that it is paid or on its way. Billing retainers on the 1st for the month ahead means you never carry a month of work on credit, and a client who leaves has already paid for the last month they received. Projects split the risk: half at signing, half on delivery.

Handle hourly work

Keep a floor for new hourly work. A legacy rate stays with the client who has it and is never quoted to anyone new.
Log time when you finish each task, not from memory at the end of the month.
Invoice within seven days of finishing the work. For ongoing hourly clients, that means the 1st.
Watch for hourly work hiding inside retainers. Divide each monthly fee by your hands-on hours for that client. If the result falls below your hourly floor, raise the price or reduce the scope.

Handle late payments calmly

Follow the same steps for every client, in the same order, and keep the tone flat and friendly. The goal is to get paid and keep the relationship, if it can be kept.

When	What happens
The due date passes	A short, friendly reminder with the invoice attached.
30 days past due	New work pauses, in writing. Nothing already built gets switched off: holding a site or an account hostage turns a late invoice into a dispute.
45 days past due	A phone call: is this timing, or has something about the work gone wrong? Agree on a written plan.
60 days past due	The engagement ends through your normal offboarding process.

Hi [name],

Invoice [number] for [month] is now 30 days past due,
so I have paused new work on your account until it is
paid. Your website and everything already built will
keep running as normal.

As soon as the payment clears, I will pick up where I
left off. If something has changed on your side, reply
and tell me. I would rather sort it out than guess.

[your name]

Keep the books current every month

Categorize every transaction and reconcile the bank account as part of the monthly routine, not in a rush at tax time.
Keep the expense list current. Software subscriptions and usage-based fees creep up quietly.
Track two cash numbers: days from finished work to invoice (aim for under seven) and days from invoice to payment (aim for under thirty).
Keep receipts attached to the transactions they belong to.

Keep business and personal money separate

Run every client payment and every business expense through a business bank account and a business card, and pay yourself by transfer on a schedule rather than spending straight from the business account. Separate accounts turn the monthly reconciliation into matching instead of guessing, keep the profit and loss line honest, and give your accountant clean records. If a personal expense lands on the business card anyway, record it as personal that same week.

Know when to bring in an accountant

I am not an accountant, and nothing here is tax advice. Talk to a qualified accountant or tax professional:

Before your first year-end, about estimated taxes, deductions, and record keeping for your situation.
Before you invoice a new kind of work. Whether website hosting, software access, or marketing services are subject to sales tax depends on the state and on how the service is described, so ask before you set up invoice items.
When you start working with clients in another state.
When you are choosing a business structure or starting to pay contractors.
Whenever a tax notice arrives that you do not fully understand.

Bring clean monthly books and your profit and loss log, and the accountant's time goes to advice instead of cleanup.

Verify it works

Every active client was invoiced on the 1st at the rate in their written agreement.
No active client is without a written rate.
Your accounting tool, deal board, and roster show the same monthly revenue.
Every below-floor retainer has a decision recorded this month.
Nothing is more than 30 days past due without the escalation step taken.
This month's profit and loss line is in the log.