Every year, I value Berkshire Hathaway (BRK.B 0.02%) (BRK.A -0.13%) using the "two-column" approach. (If you're not familiar with this approach, don't worry -- I'll explain it.) About a year ago, I found it to be about 16% undervalued at $142 per B-share. Fast-forward about a year, and the B-shares have barely advanced. So I figured it was time to sharpen up my pencil and re-estimate the value.

My conclusion: The stock is even more undervalued at today's price.

My valuation approach
Berkshire is a huge company and notoriously difficult to value. Fortunately, Buffett provides a pretty good framework for evaluating the intrinsic value. He laid it all out in his 2010 letter to shareholders. Basically, the value of Berkshire Hathaway shares comes down to two quantitative factors:

1. Investments per share
2. Operating earnings per share

Read on to see my math and assumptions, and feel free to use this two-column methodology to create your own valuation.

1. Investments per share
As of the end of 2015, Berkshire held $159,794 per A-share in investments (and about $107 per B-share). That was an 8% increase during the year. The portfolio of investments includes debt and stock in quite a few companies, but the "big four" are American Express, Coca-Cola, IBM, and Wells Fargo. Most of these investments are liquid, with reliable market prices. Thus, I simply value the investment portfolio at $107 per B-share.

2. Operating earnings per share
During 2015, Berkshire's operating businesses generated $12,304 per A-share in pre-tax earnings (or $8.20 per B-share). This represented 2% growth over the previous year.

So, what is $8.20 in pre-tax earnings per B-share worth? The S&P 500 trades at 22 times after-tax earnings, or 14 times pre-tax earnings if you assume a 33% tax rate. Some might argue that since Berkshire's collection of businesses are of higher quality than the index's, they deserve a premium. Some might also argue the index is overpriced at the moment. I won't delve into that debate, which is highly subjective by nature. I'll just be conservative and assume Berkshire's operating businesses are worth at least 10 times pre-tax earnings, or $82 per B-share.

Foolish takeaway
If I sum up $107 per B-share in investments and $82 per B-share for the operating businesses, that gives me a grand total of $189 per B-share. That's 35% more than the current trading price of $140 per B-share. That tells me Berkshire Hathaway still looks attractive, even if I calculate the value with a very conservative set of assumptions.