How to Calculate Law Firm Fees and Run Billing That Gets Paid

Two separate decisions decide whether a law firm is paid properly for its work. The first is how the fee is calculated — the model agreed with the client. The second is how billing is run — whether the work done under that model is recorded, invoiced and collected. Most firms spend their attention on the first and lose their money in the second.

This guide covers both: the four fee models in common use, how to choose between them, and a five-step billing routine that works whichever model you use.

This is general guidance on running a practice, not financial or tax advice.

The four fee models

1. Hourly rates

A rate per hour for each person who works on the matter — partner, associate, paralegal — multiplied by the time each records. It suits work whose size cannot be known in advance: arbitration, complex drafting, disputes that may settle in a month or run for two years.

Its weakness is that the client carries all the uncertainty, and its success depends entirely on time being recorded accurately. An hourly practice that reconstructs its time from memory at the end of the week is billing a guess.

2. Fixed fees

One agreed amount for a defined piece of work: incorporating a company, drafting a set of policies, filing a specific appeal. Clients like it because the cost is known. The firm carries the risk, and that risk is almost always scope: the fee was priced for one piece of work and the client gradually asks for three.

A fixed fee is only as safe as the written scope behind it — what is included, what is not, and what happens when the client asks for something outside it.

3. Retainers

A monthly or quarterly amount in exchange for an agreed volume of work — for example, a set number of advisory hours for a company each month. Retainers give the firm predictable cash flow and the client predictable access. They work best when the retainer states what happens to unused hours and how work beyond the allowance is charged.

4. Success fees

A fee, or part of one, that depends on the outcome — commonly a percentage of the amount recovered. Whether and how this is permitted varies by country and by bar rules, and the conditions can be strict. Check the rules that apply to your practice before offering one, and put the terms in writing.

Choosing a model

There is no best model, only a best fit for each matter:

• The size of the work is unknowable → hourly, ideally with an estimate or a cap the client can plan around.
• The work is well-defined and repeatable → fixed fee, with a written scope.
• The client needs ongoing advice → retainer.
• The client cannot fund the dispute and the rules allow it → a success element, usually alongside a reduced base fee.

Many firms combine them: a fixed fee for the defined stage of a matter and hourly rates beyond it. Whatever you choose, record time on every matter, including fixed-fee ones. You will not bill it, but it is the only way to know whether your fixed prices are right.

A five-step billing routine

Step 1: Record time when the work happens

The single largest source of lost revenue is time that was worked but never recorded. Short tasks — a call, a document reviewed between hearings — are the first to disappear when time is reconstructed at the end of the week. Record time against the matter as you work, with a running timer or a quick entry straight afterwards. We looked at where billable hours are lost in a separate article.

Step 2: Keep disbursements apart from fees

Court fees, expert deposits, official copies and translations are paid out on the client's behalf and must come back. They are not fee income, and mixing them into a single figure confuses both the client and your own accounts. Record each one against the matter when it is paid, keep the receipt, and show them as separate lines on the invoice.

Step 3: Send itemised invoices on a fixed cycle

An invoice that shows one large number invites questions and delays. An invoice that lists the date, the work, who did it and the time taken answers those questions before they are asked. Send on a fixed cycle — monthly, or at agreed stages — so the client is never surprised by four months of work at once.

Step 4: Make payment easy

Every extra step between receiving an invoice and paying it costs days. Let clients pay online by card, so payment can happen the moment the invoice is approved rather than when someone gets round to a bank transfer.

Step 5: Look at what is outstanding every week

Collection gets harder with age. Review unpaid invoices weekly, not monthly, and follow up early and politely. The person who chases fees in a small firm is usually also the person in court, which is why the list of what is owed needs to be in front of them rather than in a spreadsheet nobody opens.

A note on e-invoicing

Egypt, Saudi Arabia and the UAE have each introduced or announced electronic invoicing regimes run by their tax authorities, with their own registration, formatting and submission requirements. If your firm is within scope, those requirements apply to your invoices regardless of what practice-management software you use. Confirm your obligations with your tax adviser or the relevant authority — in Egypt, the Egyptian Tax Authority.

How Smart Legal OS handles this

Smart Legal OS keeps the money side on the matter:

• Time is recorded against a case, with a running timer or a manual entry, at each lawyer's own hourly rate.
• Invoices are generated from the recorded time, as itemised lines, with manual lines for disbursements and other charges and the tax rate you set.
• Clients pay by card in the client portal, and the payment is recorded against the invoice.
• The owner dashboard shows revenue, billable hours and outstanding invoices in one place.

See the full feature list, or compare plans.

Frequently asked questions

How do I persuade a client to accept hourly billing? Give an estimate or a cap at the start, and send itemised invoices that show exactly what was done. Clients object less to hourly billing than to not knowing what they are paying for.

Should junior and senior lawyers have different rates? Usually, yes. A partner's hour and a paralegal's hour are not worth the same, and a single blended rate either overcharges for routine work or undercharges for senior work. Set a rate per person.

How should I handle money paid in advance? Treat it as the client's money held against future fees and disbursements, not as income, and show clearly on each invoice how much has been applied and what remains. Rules on holding client money differ between jurisdictions, so confirm how yours must be held and accounted for.