如何選擇拆限率﹖(3)--Cost of Capital

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也許有人忍不住會問：那教科書上提到的或專家所謂的資金成本或加權平均資金成本(WACC, Weighted Average Cost of Capital)又是怎麼回事呢？我們不是應該用它做為折現率的嗎？(注意：此處所謂的「資金成本」是指對公司整體而言，而非針對某筆特定借款。)

既然我們是以巴菲特的價值投資理念為基礎，讓我們先聽聽巴菲特怎麼看所謂的「資金成本」：

Charlie and I have not the faintest idea what our cost of capital is and we think the whole concept is fairly crazy. Frankly, I’ve never seen a cost of capital that makes sense to me.---Warren Buffett

"I've listened to many “cost of capital” discussions and they've never made much sense. It's taught in business school and consultants use it, so Board members nod their heads without any idea of what's going on."
---Warren Buffett, 2001 Annual Meeting

有時巴菲特說得更直接：
“A corporation's cost of capital is 1/4 of 1% below the return on capital of any deal the CEO wants to do.”---Warren Buffett, 2001 Annual Meeting

(筆者註：表示資金成本的數字可以為了某種目的而被任意操弄出來)

Munger也曾對「資金成本」表示過意見：
"Obviously, consideration of costs is key, including opportunity costs. Of course capital isn't free. It's easy to figure out your cost of borrowing, but theorists went bonkers on the cost of equity capital. They say that if you're generating a 100% return on capital, then you shouldn't invest in something that generates an 80% return on capital. It's crazy."
--- Charlie Munger, 2001 Annual Meeting

綜而觀之，巴菲特及Munger都建議投資人最好不去理會資金成本的概念，免得走火入魔，傷了自己。既然如此，投資人也不必管它資金成本是如何計算的了。

但 不要以為他們是說「資金的成本」不重要，資金的成本很重要，只是說學術界或投資界所用的「資金成本」這個概念與定義不可取。巴菲特為了避免旗下經理人因擁 有多餘的資金而會受到各種投資案的誘惑，進而做出不理性的投資決策，因此在融資給其下公司經理人時會要求一定的利率---或是所謂的障礙率(Hurdle Rate)，來鼓勵旗下經理人把投資報酬達不到障礙率的多餘資金繳回給巴菲特做更好的運用。

巴菲特以往設定的障礙率通常為15%，對那些旗下經理人來說，取得資金的成本就是15%，在評估投資回收時自然會期望報酬率高於15%，也就是會用15%做為折現率來估算投資方案的價值。

巴菲特本人是如何選擇折現率呢？基本上他是用長期的國庫券利率做為折現率。但如利率水準太低時--例如低到3%，他會用比較高的折現率，原則上不會低於6%。因為長期而言，暫時的低利率會逐漸回歸到長期的正常利率水平。

“For our discount rate, we basically think in terms of the long-term government rate. We don't think we're any good at predicting interest rates. But in times of what seem like very low rates, we might use a little higher rate.”---Warren Buffett, 1996 Annual Meeting.

但他也提醒投資人，不管用什麼折現率，對同時間所有的投資案評估都應該用相同的利率，這樣才能相互比較。他說：

Only want one variable to compare in order to access the viability of an investment – price versus value. If we allowed discount rates to change it would lead to more than one variable. ---Warren Buffett

We want to stick with businesses we think we understand quite well and not try to have the whole panoply with all different kinds of risk rates because, frankly, we think that would just be playing games with numbers. ---Warren Buffett, 1996 Annual Meeting

另外，他建議投資人在選擇折現率時要考慮到投資持有的期間多長，如果你的投資期間是十五年，那你應該選擇十五年期的正常化(Normalized)國庫券利率做為折現率。

因此歸納起來，巴菲特對選擇折現率的建議是：

• 如果是長期投資，應該用長期的國庫券利率做為折現率。
• 不管用什麼數字，對所有的投資案應該都用相同的折現率，才可以比較。
• 關鍵不在折現率是多少，而在於預估的未來現金流量是否相當保守且確定。如果你無法很確定所估計的未來現金流量被達成的機率，折現就失去意義了。

Munger則從另個角度來看待折現率，他認為應該用機會成本(Opportunity Cost)做為折現率。他說：

“Finding a single investment that will return 20% per year for 40 years tends to happen only in dreamland. In the real world, you uncover an opportunity, then you compare other opportunities with that. And you only invest in the most attractive opportunities. It’s all about opportunity cost. The game hasn’t changed at all. That’s why modern portfolio theory is so asinine.”--- Charlie Munger, 2006 shareholders meeting.

Seth Klarman則依據不同的風險採用不同的折現率。

看來即使是大師或專家也沒有一致的看法，也可以說如何選擇折現率並沒有一個所謂正確的方法，即使是巴菲特的做法也不見得讓每一位投資人都同意。