Answer: As an initial matter, it should be emphasized that for attorney candidates that are beyond the associate stage (approximately 7-8 years out of law school), portable business is absolutely critical to their chances in the law firm market. Law firms will typically require between $300K to $3M+ in portable business from partner-level candidates, depending on the size and financials of the firm. Of course, calculating portable business is not an exact science, but rather an educated estimate. Nevertheless, it is obviously in the partner candidate's interest to provide as credible and well-founded of an estimate as possible. The following are some well-established basic guidelines for partners seeking to accurately estimate their portable business.
First, give yourself credit for what you have accomplished. Based on the negative stereotypes that lawyers share, one might expect that partner candidates are more prone to exaggerate their portable business. Actually, in my more than eight years of experience working with partners, I have found that the opposite is true. The great majority err on being too conservative, primarily because they do not want to seem to be overstating their business to prospective firms. While there are good reasons to be conservative, you don't want to fail to properly recognize the full extent of your practice or to otherwise unfairly damage your opportunities. It also does not look good to change your numbers significantly during the process, especially if the change drops you below the minimum sought by the firm.