What price margin of safety?

As the price of a stock falls below our estimate of its value, the margin of safety in buying increases.

This article is the second in an introductory series on value investing that was first published in 2006 and went on to become the core of our book Value: The Intelligent Investor's Guide to finding hidden gems on the sharemarket.
See also: 1. The essence of value investing.

et's say you’re a farmer who usually buys 10 bags of fertiliser a year. At $30 per bag, you're a happy, regular customer. Then, inexplicably, the price falls to $20.

How do you respond? To use sharemarket parlance; you back up the truck. Then you fill it with fertiliser. You were happy to buy at $30 a bag but at $20 you're ecstatic.

This is the way of the world. When the price of something we buy regularly falls, we buy more of it. Except in the sharemarket.

Here, especially among inexperienced investors, that rationale doesn't usually apply. When prices fall, many investors sell.

It's strange don't you think? Why should the sharemarket be so different to every other area of commercial life? To our minds, it isn't. What this little analogy reveals is one of the cornerstones of value investing: the difference between price and value.

Having bought hundreds of bags of fertiliser over the years, a farmer instinctively knows what a bag of particular fertiliser is really worth. If he spends $30 and gets more than that back in the quantity or quality of the crops he's growing, it's a worthwhile investment.

When the price of a particular brand falls to $20, he knows he's getting a bargain. But those who've never wielded a pitchfork wouldn't have a clue.

They don't know a bargain bag of fertiliser from a bunch of grapes because they can't assess how much using the fertiliser will add to the value of the crop at harvest time.

Price is what you pay, value is what you get

It's exactly the same with stocks, something that Benjamin Graham, seen as the founder of value investing, knew instinctively. Graham said that “price is what you pay, value is what you get”. And there's a big difference between the two.

The problem arises when investors mistake price for value. If you know what a stock is really worth then you're happy to buy more as the price falls, just as you would bags of fertiliser. This approach has become so widespread it has its own phrase, “averaging down”.

Only when one has little idea of value does one panic when the price falls. That leads us to “margin of safety”.

Margin of safety

As the price of a stock falls below our estimate of its value, the margin of safety in buying increases.

After recommending Monash IVF (ASX:MVF) as a Buy at $1.67 on September 8, 2014, the price fell to $1.08 on August 24, 2015. We continued to recommend it as a Buy because the margin of safety – the difference between price and value – had increased.

When a share price rises above our estimate of its value, as we believe it has with say Cochlear (ASX:COH), the opposite situation exists. Instead of a margin of safety in buying the stock, there's actually a margin of risk in holding onto it.

Of course, that doesn't mean that the price will fall directly after our recommendation. It may well continue to go up, as it has with Cochlear. But all that means is that the margin of risk in either holding on or buying in is increasing too.

It isn't hypocritical for us to keep calling a stock a buy as the price falls or urging you to sell when the price keeps on rising. Just as a stock can become very expensive, so too can it become very cheap.


We're as fallible as any investor in picking short-term share price movements. The fact that we recognise this and devote all our energy to identifying long-term value is what sets us apart.

We are far better judges of what a stock is actually worth than we are judges of what a collection of other people think a stock is worth. And the two are very, very different.

That brings us to the issue of establishing a stock's value, the topic of the next blog in this series on investing approaches. 

To get more insights, stock research and BUY recommendations, take a 15 day free trial of Intelligent Investor now. You can find out about investing directly in Intelligent Investor portfolios by clicking here.

Related Articles