Client billing is how a business charges clients for its work and collects the money, from choosing a pricing model to sending the invoice. Invoice templates are the easy part. The choice that moves your income comes earlier, when you pick a billing model, because that decides who pays when a project takes longer than expected.
This guide compares the four common billing models on one sample project, with the numbers worked out for a job that runs over and a job that finishes early. It then covers how to bill clients step by step, what an invoice should include, and how to get paid on time.
What is client billing?
Client billing is the process of charging a client for services and collecting payment. It covers agreeing the price, recording the work, issuing invoices, and following up until the money arrives. Service businesses such as consultancies, agencies, accounting firms, and freelancers all depend on it, because they sell time and expertise rather than a product with a fixed price tag.
The four client billing models
The table shows where each model fits and who carries the risk if the work takes longer than expected.
| Model | Best for | Who carries the risk of overrun |
|---|---|---|
| Hourly billing | Work with an unclear scope | The client |
| Fixed fee | Work you have done many times | You |
| Retainer billing | Ongoing work with regular demand | Shared, within the agreed hours |
| Milestone billing | Long projects with clear stages | You, with payment arriving earlier |
Hourly billing charges a rate for each hour worked. It is simple and fair when scope is uncertain, but the client cannot see the final price in advance, and you earn less if you get faster. Fixed fee billing sets one price for the whole job, which gives the client a known number. Your margin depends on how well you estimated. Retainer billing charges a set amount each month for an agreed number of hours or an agreed service, which gives you steady income as long as the contract says what happens to unused hours. Milestone billing splits a project price into payments tied to stages, so cash arrives as work progresses.
One project priced four ways
Here is an illustrative project. You estimate 100 hours at a billing rate of $100 an hour, and each hour costs you $50 in staff pay. The work takes 120 hours, 20% longer than estimated.
| Model and terms | Client pays | Your profit and real hourly rate |
|---|---|---|
| Hourly at $100 | 120 × $100 = $12,000 | $6,000, or $100 an hour |
| Fixed fee of $10,000 | $10,000 | $4,000, or $83.33 an hour |
| Retainer of $3,600 a month for 3 months, 40 hours a month | 3 × $3,600 = $10,800 | $4,800, or $90 an hour |
| Milestones of 30%, 40%, 30% on $10,000 | $10,000, with $3,000 at the start | $4,000, or $83.33 an hour |
Profit is what the client pays minus 120 × $50 = $6,000 in cost, and the real hourly rate is what the client pays divided by 120 hours. The 20 extra hours added $2,000 to the client’s bill under hourly billing. Under a fixed fee the client paid nothing extra, and your profit fell from the expected $5,000 to $4,000. Now look at the opposite case, where the same work takes only 90 hours and the cost falls to $4,500:
Hourly billing protects you from overruns but pays you less for speed, while fixed fees and retainers reward efficiency and punish bad estimates. So the right model depends on how well you can predict the work, which is why your own records matter. If past hours show that similar jobs took 120 hours, the 100 hour quote was the real mistake, and our article on the planning fallacy explains why that happens. For the wider picture, see our guide to project profitability metrics.
How to bill clients in 6 steps
Whichever model you use, billing clients follows the same steps, and this is also how to bill a client for the first time.
1. Agree the terms in writing
Before any work starts, put the billing model, rate or price, scope, payment terms, and what counts as extra work in a contract or signed proposal. A dispute is easier to settle when both sides can point to the same document.
2. Record the work as you do it
Log time and expenses by client and task on the day, not at the end of the month. Do this on fixed fee work too, since that is how you learn your real hourly rate. Our guide on how to track billable hours covers the details.
3. Review the hours before invoicing
Check entries against the scope, remove anything that should not be billed, and write clear descriptions. A short review can head off questions that would delay payment.
4. Create the invoice
Use a template or billing software, and include the details listed in the next section. Our free invoice templates are a simple starting point.
5. Send it on a fixed schedule
Invoice at the agreed time, such as at the end of each month or when a milestone is accepted. With a regular schedule, clients expect the bill and you avoid a long gap between doing the work and getting paid for it.
6. Follow up
Send a reminder shortly before the due date and another soon after it. Keep paid invoices in your records too. The IRS, for example, lists invoices among the documents that support a U.S. business’s gross receipts.
What to include on an invoice
Requirements differ by country, so check local rules and whether you must add VAT or sales tax details. The UK government’s list is a useful baseline. It says an invoice must include:
- A unique identification number
- Your company name, address, and contact information
- The company name and address of the customer
- A clear description of what you are charging for
- The date the goods or service were provided
- The date of the invoice
- The amounts being charged, the VAT amount if applicable, and the total owed
For client work, it also helps to add the due date, accepted payment methods, the project or purchase order reference, and a breakdown of hours and rates for hourly work.
How to get paid on time
Late payment is easier to prevent than to fix. These habits help:
- Set payment terms up front. State the number of days and any late fee in the contract.
- Ask for a deposit on new clients. The first milestone in the example above brought in $3,000 before work began.
- Make paying easy. Offer more than one payment method and put a clear due date on the invoice.
- Know your local rights. In the UK, for example, a business can charge statutory interest of 8% plus the Bank of England base rate on late business to business payments. Rules differ elsewhere.
Common client billing mistakes
-
Not defining the scope
On a fixed fee, every small extra comes out of your margin. Agree in advance how changes are priced, which also keeps scope creep under control.
-
Reconstructing hours from memory
Hours filled in at the end of the month can be guesses, and guesses are hard to defend if a client asks. Log them as the work happens.
-
Vague invoice lines
“Consulting, 40 hours” invites questions. Say what was done, and if a client wants more detail, our guide on explaining the cost of your work with reports shows how.
-
Leaving retainer terms open
Decide whether unused hours roll over or expire, and what happens when a month runs over.
-
Never checking the real hourly rate
A fixed fee can look healthy and still pay less than your hourly rate. Compare the fee with the hours after each project, then adjust your next quote.
Client billing in actiTIME
actiTIME connects tracked hours to invoices. Billing rates are set on types of work and applied to tasks, so billable amounts build up as people log time. The Billing Summary Report shows total time and billable amounts by period, you can generate PDF invoices from the same data, and the Profit/Loss Report compares billable amounts with costs, which is the real hourly rate check from the example above. Billing budgets show how much of an agreed amount has been used, and a QuickBooks Online integration can import time records for invoicing.
For other options, see our comparisons of time and billing software and invoicing software.
FAQ
What are the types of billing?
The four common types for client work are hourly, fixed fee, retainer, and milestone billing. You can also combine them, for example a fixed fee for a defined project and hourly billing for extra requests.
How do I receive payment from a client?
Send an invoice with clear payment instructions and a due date, then accept payment by bank transfer, card, or another method you agreed on. Offering more than one method makes it easier for the client to pay.
What is retainer billing?
Retainer billing means the client pays a set amount each period for an agreed amount of work or access. The contract should state the hours included, the rate for extra hours, and what happens to unused time.
Is it better to bill hourly or by project?
Bill hourly when the scope is unclear, and by project when you know the work well enough to estimate it. You can also combine the two: a fixed price for the defined part and an hourly rate for changes.
Choose the model, then check the rate
Good client billing starts before the invoice, with a model that matches how predictable the work is and terms agreed in writing. After that, record the hours and compare what you earned with the time it took, because that comparison tells you what to quote next time.
To connect tracked hours with invoices, start a free trial of actiTIME. It runs for 30 days with every feature included, and afterward you can keep the permanent free version for teams of up to 3 users.
