The PEG ratio: can a high price be justified?

2026-07-20 · By Lubin Danilo, founder of Lubin Investment

A high valuation multiple isn't always a red flag: if it comes with fast growth, it can be justified. The PEG ratio adjusts a multiple by the annual growth rate to settle the question. Applied to three real technology stocks I analyzed this week, it reveals gaps the raw multiple alone never shows, and it never works alone.

The problem the PEG ratio tries to solve

On my site, I summarize how expensive a stock is with one simple number: the P/FCF, the share price divided by the free cash flow it generates every year. A P/FCF of 345, like Datadog's right now, looks absurd at first glance. But a raw multiple only tells half the story: it compares a price to a CURRENT cash flow, without saying whether that cash flow will double next year or stagnate for a decade.

Two companies can trade at the same cash multiple and deserve opposite judgments. A company that doubles its cash generation every two years can legitimately trade at 30 times that cash: five years from now, today's price will only represent a fraction of the cash it generates by then. A company whose cash is flat doesn't deserve the same multiple: today's price stays today's price five years out, with no growth to absorb it. The PEG ratio (price/earnings to growth, which I adapt here to free cash flow) tries to answer exactly this question: is the price paid excessive, or justified by the pace of growth?

How the PEG ratio is calculated

The original formula, popularized by fund manager Peter Lynch in the 1980s, divides the P/E ratio (price divided by net income per share) by the expected annual growth rate of earnings, expressed as a percentage without the % sign. A P/E of 20 for 20% annual growth gives a PEG of 1. Lynch's rule of thumb: a PEG near 1 signals a reasonable price given the growth; below 1, the stock is potentially undervalued; well above 1, it stays expensive even after accounting for its growth.

My method never relies on net income, too easy to distort through accounting choices (depreciation, provisions, one-off items); I prefer the cash actually generated. So I adapt the calculation: I replace the P/E with the P/FCF, and earnings growth with revenue growth or free cash flow growth, whichever series is more reliable. The logic stays the same: divide a multiple by a growth percentage to see whether the price is proportionate to how fast the company is really growing.

Three valuations that all look expensive, but not to the same degree

Company	Current P/FCF	Revenue growth (5 years)	PEG	Verdict
Datadog (DDOG)	345.6x	29.5%/year	about 11.7	Expensive even growth-adjusted
Dynatrace (DT)	80.8x	22.7%/year	about 3.6	Cheapest of the three growth-adjusted, but a real trap underneath
Palantir (PLTR)	177.1x	29.1%/year	about 6.1	In between, to be taken with a grain of salt (base effect)

Take three technology companies I analyzed this week, all trading at a P/FCF in the triple digits or close to it. On the raw multiple alone, they all look equally overpriced: from 81 to 346 times their annual cash. The PEG tells a more nuanced story, and reveals a fact that would go unnoticed by looking only at the raw multiple: all three show a surprisingly similar revenue growth rate (between 22.7% and 29.5% a year), yet the market prices them at multiples that range from one to four times each other. The price paid isn't simply proportional to growth: something else, the quality of that growth, is also at play.

Datadog: the loudest multiple stays the most expensive, even adjusted

Datadog monitors, in real time, the technical health of companies' applications and infrastructure (servers, databases, networks): when a website crashes at 3 a.m., it's often a Datadog alert that wakes up the on-call engineer. The company just extended its platform to monitor AI agents and applications built on large language models, an emerging market where it was named a Leader in the Gartner Magic Quadrant for Observability for the sixth year in a row in July 2026.

Despite solid growth (revenue up more than fivefold since 2020, from $603 million to $3.43 billion), Datadog stays the most expensive of the three even growth-adjusted: a PEG near 11.7 means that, even accounting for its real growth, the market is paying nearly twelve times what a "normally valued" company would deserve for that pace of growth. One detail worth watching: stock-based compensation reached $750 million in 2025, about 75% of the free cash flow generated that same year. A significant share of the cash "earned" therefore goes toward offsetting shareholder dilution rather than funding growth or returning cash to shareholders.

Dynatrace: a moderate PEG hiding a real trap

Dynatrace sells a competing monitoring platform built around Grail, its unified data lakehouse combining logs, metrics, and application traces, and Dynatrace Intelligence, an AI layer launched in 2026 that combines deterministic analytics with generative AI to automatically diagnose an outage. The company crossed $2 billion in annual recurring revenue (ARR) and delivered a fourth consecutive quarter of 16% constant-currency ARR growth.

On paper, Dynatrace shows the lowest PEG of the three (about 3.6), which would suggest the "least unreasonable" valuation. But one number contradicts that quick read: my free-cash-flow-per-share growth criterion fails for Dynatrace, at -0.7% a year over five years, even though its gross free cash flow more than doubled over the period (from $206 million to $433 million). The explanation comes down to one word: dilution. Share count rose every year to fund stock-based compensation, which nearly quadrupled over the period (from $58 million to $272 million). Once that compensation is stripped out, the cash actually available per share is flat, even as the company's gross cash clearly rises. A PEG calculated only on revenue growth completely masks this trap: it looks at the top line of the income statement, not what's actually left for each shareholder.

Palantir: the most spectacular growth, to be weighed against a base effect

Palantir sells data analytics software to governments (the US Army, immigration enforcement, intelligence agencies, the UK Ministry of Defence, which awarded it a £240 million contract in 2025) and, increasingly, to companies through its AIP artificial intelligence platform. In Q1 2026, US commercial revenue jumped 133% year over year, and the remaining US commercial deal value climbed 145% to $4.38 billion, a signal of future revenue already booked.

Palantir's PEG (about 6.1) looks like it sits between Datadog and Dynatrace, but it hides a distortion specific to this company: in 2020, its free cash flow was negative (-$309 million). The company went from a cash-burning machine to a 37.5% free cash flow margin in 2025, one of the best in software. Computing a compound annual growth rate from a negative or near-zero starting point produces huge, barely comparable numbers (my free-cash-flow-per-share growth measure comes out at several hundred percent a year over this period, a figure it would be dishonest to plug straight into a PEG). I therefore preferred the more stable revenue growth for this calculation. One genuine quality signal behind this number: stock-based compensation fell from $1.27 billion in 2020, more than that year's entire revenue, to $684 million in 2025, a meaningfully improved capital discipline even though dilution remains real (+7.6% shares outstanding per year over five years).

The PEG ratio's blind spots, what it never tells you

The PEG has three blind spots worth knowing before relying on it. First, it becomes unusable once growth turns negative or near zero: dividing a multiple by a negative number produces a negative PEG, meaningless to interpret (a declining company is never "cheap" in PEG terms, whatever its multiple). Second, the choice of growth rate radically changes the result: revenue growth, earnings growth, free cash flow growth, over one year or five, forward-looking or trailing. The examples above show that the same choice of denominator can mask an opposite reality, as with Dynatrace. Finally, the PEG says nothing about the QUALITY of growth: growth funded by massive dilution, ballooning debt, or shrinking margins isn't worth the same as self-funded growth with expanding margins, even when the PEG shows an identical number in both cases.

How I use the PEG in my method

I never turn the PEG into a scoring criterion on its own, and it doesn't enter my quality score out of 10. I use it as a quick consistency check, once a company's quality is already established through my usual ten criteria (margins, sales and cash growth, buybacks, debt, return on invested capital): does the company's real growth justify, even roughly, the multiple gap versus the rest of the sector? If the PEG stays extreme after that check, it's a flag to dig further, not a reason to decide automatically. The real decision in my method stays the same as always: place the current multiple within the company's own five-year valuation history (its percentile) and understand why the market is paying that price, before judging whether it's justified.

The PEG ratio divides a valuation multiple by an annual growth rate to judge whether a high price is justified by growth.
I adapt the classic formula (P/E ÷ earnings growth) to my method: P/FCF ÷ revenue growth or free cash flow growth.
Across Datadog, Dynatrace, and Palantir, the PEG ranges from 3.6 to 11.7 even though their revenue growth rates are surprisingly close: the price paid doesn't depend on growth alone.
The PEG becomes misleading with negative growth, near-zero growth, or growth funded by heavy dilution (the Dynatrace case).
I never use it alone: always combined with the company's underlying quality and its valuation percentile within its own history.

FAQ

What exactly is the PEG ratio?

The PEG ratio (price/earnings to growth) divides a valuation multiple by a company's expected annual growth rate, expressed as a percentage without the % sign. It's used to judge whether a high multiple is justified by fast growth, or stays excessive even after accounting for that growth.

Why use P/FCF instead of the P/E ratio in the calculation?

The P/E ratio relies on GAAP net income, which depreciation choices or one-off items can distort. My method judges a company on free cash flow, the cash actually generated once all bills are paid, so I adapt the PEG by replacing the P/E with the P/FCF.

Does a PEG near 1 mean you should buy the stock?

No. A PEG near 1 only signals that the price looks proportionate to current growth. It says nothing about the quality of the business, how durable that growth is, or dilution risk. It's a consistency check, never a buy signal on its own.

Why does Dynatrace's PEG look low when its cash-per-share growth is disappointing?

Because the calculation uses revenue growth, which is progressing well, while the growth of cash actually available per share is held back by dilution tied to stock-based compensation. The PEG doesn't capture this gap between the top and the bottom of the income statement.

Which growth rate should you use in a PEG calculation?

There's no single rule. I favor free-cash-flow-per-share growth when the series is stable and meaningful, and fall back on revenue growth when free cash flow is too recent, too volatile, or starts from a negative base (like a company that just turned profitable).

About the author

Written by Lubin Danilo, founder of Lubin Investment. A self-taught individual investor, I find fundamental analysis fascinating, and it has delivered excellent results. For three years now, my performance has beaten the S&P 500. But analyzing every stock took too much time: sites with incomplete data, calculation methods and criteria never aligned with mine. And spotting the best stocks was just as time-consuming, even with my own well-defined checklist. So I put my software development background to work to build this software, base my investment strategy on its results, and share it with people who share the same passion as me. It judges a company's quality and its price separately, using criteria drawn from the financial literature (Warren Buffett, Michael Mauboussin, Aswath Damodaran).