Numbers can lie -- but they're the best first step in determining whether a stock is a buy. In this series, we use some carefully chosen metrics to size up a stock's true value based on the following clues:

  • The current price multiples.
  • The consistency of past earnings and cash flow.
  • How much growth we can expect.

Let's see what those numbers can tell us about how expensive or cheap Zix (Nasdaq: ZIXI) might be.

The current price multiples
First, we'll look at most investors' favorite metric: the P/E ratio. It divides the company's share price by its earnings per share -- the lower, the better.

Then, we'll take things up a notch with a more advanced metric: enterprise value to unlevered free cash flow. This divides the company's enterprise value (basically, its market cap plus its debt, minus its cash) by its unlevered free cash flow (its free cash flow, adding back the interest payments on its debt). Like the P/E, the lower this number is, the better.

Analysts argue about which is more important -- earnings or cash flow. Who cares? A good buy ideally has low multiples on both.

Zix has a stunningly low P/E ratio of 3.9 and an EV/FCF ratio of 15.4 over the trailing 12 months. If we stretch and compare current valuations to the five-year averages for earnings and free cash flow, Zix has a P/E ratio of 31.9 and a five-year EV/FCF ratio of 70.4.

A positive one-year ratio under 10 for both metrics is ideal (at least in my opinion). For a five-year metric, under 20 is ideal.

Zix has a mixed performance in hitting the ideal targets, but let's see how it compares against some competitors and industry mates. 

Company

1-Year P/E

1-Year EV/FCF

5-Year P/E

5-Year EV/FCF

Zix 3.9 15.4 31.9 70.4
Cisco Systems (Nasdaq: CSCO) 16.1 7.4 14.2 7.8
EMC (NYSE: EMC) 21.3 11.1 30.3 15.1
salesforce.com (NYSE: CRM) 4,876.3 157.1 416.8 89.4

Source: S&P Capital IQ.

Numerically, we've seen how Zix's valuation rates on both an absolute and relative basis. Next, let's examine...

The consistency of past earnings and cash flow
An ideal company will be consistently strong in its earnings and cash flow generation.

In the past five years, Zix's net income margin has ranged from -44.6% to 120.8%. In that same time frame, unlevered free cash flow margin has ranged from -12.7% to 26.8%.

How do those figures compare with those of the company's peers? See for yourself:

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Source: S&P Capital IQ; margin ranges are combined.

Additionally, over the last five years, Zix has tallied up two years of positive earnings and two years of positive free cash flow.

Next, let's figure out...

How much growth we can expect
Analysts tend to comically overstate their five-year growth estimates. If you accept them at face value, you will overpay for stocks. But while you should definitely take the analysts' prognostications with a grain of salt, they can still provide a useful starting point when compared to similar numbers from a company's closest rivals.

Let's start by seeing what this company's done over the past five years. Because of prior losses, Zix's trailing EPS growth rate isn't meaningful. Here's how its peers have done:

Source: S&P Capital IQ; EPS growth shown.

And here's how it measures up with regard to the growth analysts expect over the next five years:

Source: S&P Capital IQ; estimates for EPS growth.

The bottom line
The pile of numbers we've plowed through has shown us the price multiples shares of Zix are trading at, the volatility of its operational performance, and what kind of growth profile it has -- both on an absolute and a relative basis.

The more consistent a company's performance has been and the more growth we can expect, the more we should be willing to pay. We've gone well beyond looking at a 3.9 P/E ratio, and we see that its EV/FCF ratio is a more moderate 15.4. Why the difference? It's because Zix's earnings are deceptively high because of a massive tax benefit. That's also why you see the top end of Zix's margin range at 120.8%. In other words, because of the tax accounting, Zix had more earnings in the last 12 months than sales!

When we look over a five-year period, Zix's price multiples are high. This is because it's only now swinging to profitability. Zix certainly isn't as cheap as its 3.9 P/E ratio would indicate, but interested potential investors need to next determine whether Zix can stay profitable and grow from here.

If you find Zix's numbers or story compelling, don't stop. Continue your due diligence process until you're confident one way or the other. As a start, add it to My Watchlist to find all of our Foolish analysis.

To see the stocks that I've researched beyond the initial numbers and bought in my public real-money portfolio, click here.

Anand Chokkavelu owns shares of Cisco. The Motley Fool owns shares of Cisco Systems and EMC. The Fool owns shares of and has created a bull call spread position on Cisco Systems. Motley Fool newsletter services have recommended buying shares of salesforce.com and Cisco Systems. Motley Fool newsletter services have recommended shorting salesforce.com. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.