Under ABA Formal Opinion 512, lawyers billing hourly may bill only for actual time spent, which includes time prompting, reviewing and verifying AI output but not time saved. Flat fees must remain reasonable, so a fee set before AI efficiencies may need review. Lawyers generally should not charge clients for learning general AI tools. The cost of general-purpose AI built into firm software is overhead; a third-party tool used for a specific matter may be charged as an expense if reasonable and agreed in advance.
The rule in one line
Rule 1.5 requires reasonable fees. ABA Formal Opinion 512 applies that rule to AI: bill what you actually did, charge fairly for what you used, and do not pass on the cost of learning.
Hourly billing: actual time only
A lawyer billing by the hour must bill for actual time. If AI produces a first draft in minutes and you spend an hour refining and checking it, you bill the hour, not the half-day the task used to take.
What counts as billable:
- Time spent crafting prompts for the specific matter.
- Time spent reviewing, editing and verifying the output, including checking every citation.
- Time spent applying judgment to what the AI produced.
What does not:
- Time you would have spent without AI but did not.
- Time spent learning how to use a tool you will use across your practice (unless the client asked you to use that specific tool).
Model the numbers for a real task with our AI Fee Fairness Calculator.
Flat fees: reasonableness still applies
Opinion 512 indicates that a flat fee can become unreasonable if AI lets the lawyer complete the work far more quickly than the fee contemplated. That does not mean flat fees must fall every time you get faster. It means you should review fees periodically and be able to justify them by the value and quality delivered.
For many firms, AI makes alternative fees more attractive: clients get price certainty, and the firm keeps the benefit of efficiency within a fee that remains reasonable.
Charging for AI tools
| Cost | Treatment under Opinion 512 |
|---|---|
| General-purpose AI built into your software (for example, an assistant in your office suite) | Overhead; not charged to clients |
| A third-party AI tool used for a specific client matter (for example, per-use document review) | May be charged as an expense where reasonable and agreed |
| Time learning a general tool | Not charged, unless the client requested that tool |
Disclose any expense pass-through in advance and in writing.
What to put in your engagement letter
Explain, briefly and clearly:
- That you use AI tools to assist with certain tasks, under lawyer supervision.
- That you bill only actual time on hourly matters, including review time.
- How AI tool costs are treated (usually overhead).
- That clients can ask about AI use on their matter.
Our Client AI Disclosure Clause Generator drafts this wording.
State guidance on fees
Several states have addressed fees as part of their AI guidance, and Virginia’s Legal Ethics Opinion 1901 (November 2025) focuses specifically on reasonable fees where AI is used. Check your jurisdiction in the State Bar AI Guidance Navigator.
The opportunity
The billable hour rewards time; AI rewards outcomes. Firms that reprice around value, measure where AI saves time and reinvest that time in client service tend to benefit most. Estimate your firm’s potential with the Legal AI ROI Calculator.
Sources
Frequently asked questions
Can I bill the time AI saved me?
Not on an hourly matter. Opinion 512 indicates hourly fees must reflect actual time. The efficiency benefits the client.
Can I charge clients for my ChatGPT or Claude subscription?
Generally no. General-purpose AI tools used across your practice are overhead. Costs of a third-party tool used specifically for a client’s matter may be charged where reasonable and disclosed in advance.
Is time spent checking AI output billable?
Yes. Reviewing and verifying AI output is genuine legal work, and Opinion 512 requires appropriate verification.
Should I move to flat fees because of AI?
Many firms are exploring flat and value-based fees so that efficiency benefits both firm and client. Fees must still be reasonable under Rule 1.5, and flat fees set before AI may need review.
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This article is general educational information, not legal advice. Rules differ by jurisdiction and change often; check the primary sources and your own professional rules before relying on it.