"Retainer" is one of the most misused terms in legal billing. Clients think it means they've locked in your time for a month. Some attorneys think it means they can spend the money immediately. Both are wrong in most cases, and the resulting confusion creates ethics problems.

Here's exactly what a retainer is, how it works, and how to set one up without creating problems down the road.

This post is part of our billing series for law firm owners. For the full financial setup framework when starting a firm, see How to Start a Law Firm in 2026.

The Two Types of Retainer

The word "retainer" covers two different arrangements that work very differently:

1. Advance Fee Deposit (What Most People Mean)

The client pays money upfront. You hold it in your IOLTA trust account. As you do work, you transfer earned fees from trust to your operating account. This is the most common type of retainer in consumer and small business legal work. The money belongs to the client until you earn it.

2. General Retainer (Availability Fee)

The client pays a fee specifically to ensure you're available to them, not as a deposit against future work. This fee is earned when paid and goes directly into your operating account. General retainers are less common, typically used by corporate clients who want guaranteed availability of a specific attorney, and governed by specific bar rules that vary by state.

When someone asks "what's your retainer?" they almost always mean the advance fee deposit. The rest of this guide covers that type.

How an Advance Fee Retainer Works

The mechanics are straightforward:

  1. Client signs your engagement letter and retainer agreement.
  2. Client pays the retainer amount. The payment goes into your IOLTA trust account, not your operating account.
  3. You do work on the matter and bill the client (typically monthly).
  4. You transfer the billed amount from the trust account to your operating account, after providing the client with a statement showing the transfer.
  5. The trust balance decreases until it reaches a replenishment threshold (defined in your engagement letter) or is exhausted.

The key point: the money in your trust account is not your money until you earn it and properly transfer it. Using it before earning it, or mixing it with your operating funds, is a trust account violation that can result in discipline. For a full explanation of trust account rules, see IOLTA Trust Accounts Explained for New Law Firms.

How Much to Charge as a Retainer

There's no universal rule, but there's a useful formula: your retainer should cover 1-2 months of expected billing on the matter.

For a divorce expected to involve 15-20 hours at $300/hour, a $4,500-$6,000 retainer is appropriate. For complex commercial litigation where monthly billing might run $10,000-$30,000, the initial retainer might be $25,000-$50,000 to ensure you have sufficient cushion before requiring replenishment.

Setting the retainer too low creates a situation where you're constantly asking for replenishment, which irritates clients and creates collection risk. Setting it too high prices you out of matters where clients comparison-shop.

Practice area norms vary significantly. In personal injury, retainers are essentially non-existent (contingency is standard). In estate planning, retainers are typically modest ($1,500-$3,000). In litigation, they're often substantial ($10,000+). Know what's customary in your area and practice type, and use your engagement letter to explain clearly how the retainer works.

What Your Retainer Agreement Must Include

A retainer agreement is separate from or incorporated into your engagement letter. At minimum, it needs to address:

Many attorneys incorporate this directly into the engagement letter. Others use a separate document. Either works, but the terms need to be in writing before you take the money.

Replenishment Clauses

A replenishment clause in your engagement letter is not optional for ongoing matters. It specifies that when the trust balance falls below a threshold (typically 50% of the initial retainer), the client agrees to replenish to the original amount within a defined timeframe.

Without a replenishment clause, you'll be billing against a dwindling retainer balance, eventually exhausting it, and then either working without a cushion or having a difficult conversation about payment. Address it upfront in the engagement letter so the expectation is set before the problem occurs.

Refund Obligations

If you're holding an advance fee deposit and the representation ends while there are unused funds in trust, you must refund the unearned portion. This is not discretionary. The money belongs to the client until you earn it.

The refund must come from your IOLTA account, not your operating account. Document the refund with a closing trust statement showing the final balance and the refund amount. Keep records. Trust account record-keeping is an ethics requirement in every state.

General retainers (availability fees) are treated differently: they're typically earned when paid and non-refundable. But you must specify this explicitly in the engagement letter, and some states have specific rules on when general retainers are permissible. Check your state bar's rules before using a general retainer structure.

Common Retainer Mistakes

Billing setup is one of the places new law firms get into ethics trouble without intending to. The rules around trust accounts are strict and enforced. For a complete picture of what goes in trust and what doesn't, see IOLTA Trust Accounts Explained. For how billing fits into a billing model decision, see Hourly vs Flat Fee Billing.

Law firms that get billing right from day one collect faster, have fewer disputes, and spend less time on collections. The systems that handle retainer collection, trust transfers, and invoice follow-up automatically are the same systems that let attorneys spend more time on billable work. If you want to see how that works for a firm like yours, book a free audit call.