A partner once told me she'd accepted a lateral offer built almost entirely around her book of business, only to find, three months after starting, that nearly a third of it was conflicted out at the new firm. The clients hadn't changed. The math on the offer had been wrong from the start.
"Portable book of business" is one of the most load-bearing phrases in lateral recruiting, and one of the least interrogated. It sounds like a fact about you. In practice, it's closer to a projection — and a fragile one, dependent on conflicts, client consent, and relationships that may not travel as cleanly as either side assumes.
What "Portable" Actually Requires
A book doesn't move on its own. For it to actually transfer, a few things generally have to hold up:
Conflicts clearance: the new firm's existing client roster may conflict with some of your relationships, sometimes in ways that aren't obvious until a formal check is run. This should happen before an offer is finalized, not after you've resigned from your current firm.
Client consent and relationship strength: some clients follow a specific lawyer without hesitation. Others are institutionally tied to the firm, not the individual, and won't move regardless of the relationship. Knowing which of your clients fall into which category — honestly, not optimistically — matters more than the aggregate revenue number.
Non-compete and notice provisions: depending on jurisdiction and firm, there can be real constraints on solicitation during a transition period. This varies significantly by state and by country, and it's worth understanding precisely rather than assuming it works the same way everywhere.
Origination credit on shared or referred matters: if part of your book originated through another partner or a cross-referral, the new firm's expectations about who gets credit for that going forward may not match your assumptions.
The Questions That Separate a Real Number From an Optimistic One
Before treating a book of business figure as a settled part of the offer, it's worth pressure-testing it directly:
● Has the firm run a formal conflicts check against your actual client list, not a general sense of your practice area?
● What percentage of the projected book is the firm treating as "confirmed" versus "expected to follow"?
● What support exists — from the firm's business development or conflicts team — during the transition period itself?
● If a portion of the book doesn't transfer, does the compensation structure adjust, or is the offer fixed regardless of outcome?
Firms that have done this kind of lateral hire well will usually have already run the conflicts analysis before making the offer. If they haven't, that's worth noticing.
A Book Is a Relationship, Not a Line Item
Treating portable business as a guaranteed asset rather than a set of relationships that need to survive a transition is one of the most common reasons a lateral move underperforms its projected economics. The firms that get this right treat the diligence as seriously as the candidate does.
This is the third in a four-part series on what lateral moves and partnership offers actually involve beyond the title and headline number. Sonder Consultants places senior associates, counsel, and partners at elite firms across the US, UK, Hong Kong, and Australia — including running conflicts-aware book analysis before an offer is finalized.
