A retainer letter is the written agreement that formally hires a professional, usually an attorney, and sets out the terms of the relationship: what work will be done, what it will cost, what you are expected to pay upfront, and how either side can end things. It turns an initial conversation into a binding arrangement, and it is specific enough to head off the misunderstandings that otherwise end in fee disputes or malpractice claims. Some professionals call it an engagement letter. The function is the same.
Without one, nobody has a clean record of what was agreed. A verbal arrangement may technically create a relationship, but proving its terms after a disagreement is slow and expensive. The letter is the fix.
What a Retainer Letter Should Cover
A well-drafted retainer letter addresses several categories of terms. Some are required by professional ethics rules. Others are simply good practice.
Scope of Representation
The scope clause is arguably the most important part of the document. It defines exactly what the professional will and will not do. For an attorney, that might be “represent you in the breach-of-contract lawsuit filed in federal court” rather than a vague “handle your legal matters.” Narrowing the scope protects the professional from being expected to handle unrelated issues, and it protects you by making clear what you are paying for. If the matter expands later, the letter should be amended in writing.
Fees
ABA Model Rule 1.5 requires that attorney fees be reasonable and that the basis for the fees be communicated to the client in writing before, or shortly after, representation begins.1American Bar Association. Rule 1.5 Fees Most retainer letters use one of three structures:
- Hourly billing, where the professional charges a set rate per hour worked. Rates vary widely by practice area, market, and experience.
- Contingency fees, where the professional takes a percentage of what you recover, typically in the 25% to 40% range, often with the percentage rising if the case goes to trial. Contingency arrangements must be in writing and must clearly explain how expenses are deducted from the recovery.
- Flat fees, a single predetermined amount for a defined task like drafting a will, forming a business entity, or handling an uncontested divorce. The letter should state when the flat fee is considered earned, whether on completion or at some earlier milestone.
The distinction between when a fee is earned and when it is paid matters. Money paid in advance for hourly work remains your property until the professional actually performs the work. A “true retainer,” by contrast, pays the professional to be available during a specified period and is considered earned the moment it is paid. The letter should make clear which type of arrangement applies. Confusing the two is one of the most common sources of fee disputes.
Costs and Expenses
Beyond professional fees, you are usually responsible for out-of-pocket costs the professional incurs on your behalf: court filing fees, process servers, expert witnesses, copying and postage, and travel for depositions or hearings. The retainer letter should say whether these are drawn from your deposit as they come up or billed separately on a monthly invoice.
Communication and Billing
Good retainer letters set expectations for how and how often the professional will communicate. Some specify a preferred method of contact, which increasingly matters for cybersecurity reasons; email may not be appropriate for highly sensitive matters. The letter should also describe the billing cycle, which is typically monthly, what detail invoices will contain, and any late-payment interest or penalties. Many states cap the interest rate professionals can charge on overdue invoices, so these terms need to comply with local law.
Malpractice Insurance Disclosure
A growing number of states require attorneys to tell clients in writing whether they carry professional liability insurance. The specifics vary. Some states require disclosure only if the attorney lacks coverage; others mandate annual reporting to the state bar regardless. If your retainer letter includes an insurance disclosure, read it. An uninsured attorney who makes a serious error may not have the resources to compensate you. If the letter does not mention insurance at all, it is worth asking.
The Deposit and the Trust Account
Most professionals ask for an upfront deposit before starting work. In everyday language this is often called the “retainer,” though technically it is an advance fee. The money goes into a dedicated trust account, not the professional’s personal or business account. Ethics rules in every state require this separation.1American Bar Association. Rule 1.5 Fees The professional withdraws from trust only as fees are earned or expenses are incurred, and must be able to account for every dollar at any time.
The size of the initial deposit depends on the complexity of the matter and the anticipated workload. A straightforward contract review might require a few thousand dollars; complex commercial litigation can call for $10,000 or more. The retainer letter should state the initial deposit amount, the conditions under which the professional can draw from it, and whether you will be asked to replenish the account if the balance drops below a certain threshold.
When the Relationship Officially Starts
Once both sides are satisfied with the terms, the letter is signed on paper or through an electronic signature platform. That signature creates a permanent record of the date the relationship officially began, which matters for statute-of-limitations calculations, insurance coverage triggers, and court filings. You then submit the initial deposit. Work begins once the professional has both the executed letter and the funds in trust. You should receive a fully signed copy for your records.
Changing or Ending the Engagement
Legal matters rarely unfold exactly as planned. When the scope needs to change or the fee structure no longer fits, the retainer letter should be amended in writing. A handshake modification invites the same problems the original letter was designed to prevent.
If the Professional Wants Out
Professionals cannot simply walk away. ABA Model Rule 1.16 governs when a lawyer may or must withdraw and generally requires that the withdrawal not leave the client worse off at a critical moment.2American Bar Association. Rule 1.16 Declining or Terminating Representation If the matter is in active litigation, the attorney often needs court permission to withdraw. The departing professional must take reasonable steps to protect your interests, including giving notice, allowing time to find replacement counsel, and handing over the file.
If You Want Out
You can fire your attorney at any time, for any reason. You don’t need permission. But termination doesn’t erase obligations that have already accrued. You still owe for work performed and costs already incurred. The retainer letter should spell out the final accounting: any unearned fees remaining in trust come back to you, and the professional must hand over your file promptly enough that no deadlines are missed during the transition to new counsel.3American Bar Association. A Lawyers Obligation to Convey Information to a Former Client or Successor Counsel
File Retention After the Engagement Ends
Ethics rules generally require attorneys to preserve client file materials for a reasonable period after representation ends. A five-year retention period stated in the retainer letter is a common benchmark for civil matters. Criminal defense files may need to be kept much longer, potentially for the duration of a client’s sentence. The letter should address this so both sides know what to expect.
Fee Dispute Clauses
Disagreements over fees are one of the most common friction points between clients and professionals. Many retainer letters include a dispute resolution clause requiring mediation or arbitration before either side can file a lawsuit. Most state and local bar associations also run fee arbitration programs that offer a faster, cheaper alternative to court. In some states, arbitration is mandatory for the attorney if the client requests it.
If your retainer letter contains a mandatory arbitration clause, understand what you are agreeing to. Arbitration can be faster and less expensive than litigation, but it also limits your right to appeal. Read the clause carefully before signing, and ask which arbitration rules will apply and who bears the costs of the proceeding.
Going Without One
Proceeding without a written retainer letter is a gamble for both sides. You have no documented basis for challenging a bill that seems inflated or disputing the scope of work. The professional has a harder time collecting unpaid fees without written proof of the agreed rate. Courts that later need to sort out the relationship will look at emails, phone records, and conduct to piece together an implied agreement, which is expensive and uncertain. Some jurisdictions treat the absence of a written fee agreement as grounds for reducing or denying a professional’s fee claim entirely. The retainer letter exists to avoid all of this, and the few minutes it takes to read and sign one is time well spent.