Most law firms I talk to can tell me their monthly ad spend. Almost none can tell me their cost per retained client with any accuracy.
This isn’t a criticism — it’s a structural problem. Legal marketing data lives in three or four different systems that don’t talk to each other: your ad platforms, your call tracking tool, your intake software, and your CRM. Connecting them manually is enough work to make anyone give up.
But without knowing your true client acquisition cost, you can’t make rational decisions about your marketing budget. Here’s how to calculate it.
The Formula
Cost Per Retained Client = Total Marketing Spend ÷ Number of Retained Clients
Simple in principle. The hard part is making sure “total marketing spend” captures everything, and “number of retained clients” is correctly attributed to the right time period and channel.
What to Include in “Total Marketing Spend”
Most firms only count their media spend (what they paid Google, Meta, or their SEO agency). Here’s the complete list:
- Paid media: Google Ads, Meta Ads, LSA, display campaigns
- Agency/vendor fees: The SEO firm, the PPC manager, the content agency
- Technology: Call tracking (CallRail), landing page tools, CRM licenses used for marketing
- Internal labor: The paralegal who manages intake, the marketing coordinator’s time
- Print and event marketing: Billboards, sponsorships, bar association events
Most firms are shocked to find their actual spend is 30–50% higher than their media spend alone.
Calculating by Channel
Aggregate CPRC is useful. Channel-level CPRC is where the real decisions get made.
Build a simple table:
| Channel | Monthly Spend | Retained Clients | CPRC |
|---|---|---|---|
| Google Ads (Search) | $8,500 | 12 | $708 |
| Google LSA | $2,200 | 5 | $440 |
| SEO (agency + content) | $3,500 | 8 | $437 |
| Meta Ads | $1,800 | 2 | $900 |
| Referrals | $0 | 6 | $0 |
This table alone changes the conversation. Meta looks cheap until you see a $900 CPRC. Referrals look free until you realize you should be investing in a referral development program.
Weighting by Case Value
If your practice handles multiple case types, weight by average case value, not just client count. A personal injury CPRC of $1,200 might be excellent. A traffic ticket CPRC of $1,200 is catastrophic.
True ROI = (Average Case Value × Number of Clients) ÷ Total Marketing Spend
Track this monthly, by channel, by practice area. The first time you run this calculation, you’ll almost certainly reallocate your budget.
The firms that grow predictably are the ones that treat marketing like a financial function, not a creative one. They know their numbers, they optimize toward ROI, and they let the data make the hard decisions. If you don’t have the infrastructure to calculate this automatically, that’s the first problem worth solving.