When a company owns more than 50% of another company, U.S. accounting rules state that the parent company has to consolidate its books. In other words, the parent company reflects 100% of the assets and liabilities and 100% of financial performance (revenue, costs, profits, etc.) of the majority-owned subsidiary (the “sub”) on its own financial statements. But since the parent company does not 100% of the sub, the parent company will have a line item called minority interest on its income statement reflecting the portion of the sub’s net income that the parent is not entitled to (the percentage that it does not own). The parent company’s balance sheet will also contain a line item called minority interest which reflects the percentage of the sub’s book value of equity that the parent does NOT own. It is the balance sheet minority interest figure that we add in the Enterprise Value formula.
Now, keep in mind that the main use for Enterprise Value is to create valuation ratios/metrics (e.g. EV/Sales, EV/EBITDA, etc.) When we take, say, sales or EBITDA from the parent company’s financial statements, these figures due to the accounting consolidation, will contain 100% of the sub’s sales or EBITDA, even though the parent does not own 100%. In order to counteract this, we must add to Enterprise Value, the value of the sub that the parent company does not own (the minority interest). By doing this, both the numerator and denominator of our valuation metric account for 100% of the sub, and we have a consistent (apples to apples) metric.
One might ask, instead of adding minority interest to Enterprise Value, why don’t we just subtract the portion of sales or EBITDA that the parent does NOT own. In theory, this would indeed work and may in fact be more accurate. However, typically we do not have enough information about the sub to do such an adjustment (minority owned subs are rarely, if ever, public companies). Moreover, even if we had the financial information of the sub, this method is clearly more time consuming.