How is income imputed to a spouse that's not working?

In the case of Schmachtenberg v. Schmachtenberg, 34 So.3d 28 (Fla. 3rd DCA 2010), the appellate court gives us guideance on how to correctly impute income to a wife that has raised children and supported her husband during a marriage:

            The trial court, when determining the amount of alimony that the Husband should pay in a modification case, imputed $18,000 in income to the Wife. This was the same amount that the parties agreed to impute to her in 2002 in their Marital Settlement Agreement. On appeal, the District Court held that because the "projected and estimated" income imputed to the Wife in the marital settlement agreement did not come to fruition the amount should not have been imputed to her:

1. "There is no dispute that [the Wife] is currently unemployed and has engaged in no meaningful employment since the parties' divorce in 2002. The undisputed record is, therefore, that her current income in $0. Rather than using that number as a basis for determining need and thus the amount of alimony [the Husband] should currently pay, the court below imputed $18,000 in income to [the Wife], which is the amount the parties agreed to impute to her in 2002 when they executed their marital settlement agreement ."

2. "The record in this case is that while [the Wife] has both a college degree and a real estate license, she has not held meaningful full-time employment since the 1970's. The last meaningful part-time employment she enjoyed was in [the Husband's] law office where she assisted in real estate related work." 

3. "[The Wife] has sold only two properties as a real estate agent and has spent most of her time assisting the parties' disabled son. Other than this, there is no evidence that, now at age 58 and many years outside the workplace, [the Wife] is employable except as a real estate agent. As to this (or for that matter any other) line of work, there is no evidence whatsoever as to the current job market or as to the prevailing earnings level for such agents in the community where [the Wife] lives. Absent such evidence, income could not be imputed to her."

4. "The amount imputed to [the Wife] in the 2002 marital settlement agreement, as the agreement itself confirms, did not represent her actual income, but represented no more than an estimate of potential future earnings…. As we know, the 'projected and estimated' income imputed to [the Husband] in this agreement did not come to fruition; nor, as the record confirms, did [the Wife's]. This estimate should not, therefore, have been attributed to her now for the purpose of determining either alimony or child support."