ACM vs STN: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of August 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

Reading it: ACM is the cheaper of the two on forward earnings, but cheaper is not the same as better. Pair the valuation with growth (how far the forward P/E sits below the trailing P/E) and risk (beta) before you decide.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. ACM and STN share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined ACM and STN exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

AECOM is in the business of engineering expertise, not steel. The company plans, designs, engineers and manages infrastructure programs for governments and large corporations: highways and transit systems, water and wastewater treatment, airports and ports, environmental remediation, flood defenses, and increasingly the power and site work behind data centers. It reports in three segments, Americas (about $2.9 billion of quarterly revenue), International (about $890 million), and a small AECOM Capital investment arm, and employs roughly 51,000 people. Critically, AECOM exited self-perform construction years ago, so it no longer takes fixed-price building risk on its own balance sheet. What is left is a professional services business with very little capital intensity, which is why return on equity runs near 29% on only about $3.35 billion of debt against $1.04 billion of cash.

Full ACM guide

Stantec sells professional services, not products. Roughly 32,000 engineers, architects, scientists and planners bill time on projects across five business lines: Water, Environmental Services, Infrastructure, Buildings, and Energy & Resources, reported in three geographic segments (United States, Canada and Global). The work is unglamorous and specific: designing water and wastewater treatment upgrades, transit and highway projects, hospitals, semiconductor and advanced-manufacturing plants, permitting and remediation studies. Clients skew public sector, so revenue follows municipal, state, provincial and national capital programs. Recent examples show the shape of it: Stantec was named a preferred bidder as a primary designer on the multibillion-pound Scottish Water investment program, and in May 2026 joined a joint venture to deliver Greater Western Water's infrastructure program in Australia.

Full STN guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• ACM drivers: A record backlog that is growing faster than revenue; Margin expansion in an asset-light model.
• STN drivers: Water and wastewater capital cycles; Record backlog converting to billable hours.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: The cash flow problem is the live issue and it is not resolved: operating cash flow fell 98% in the fiscal second quarter of 2026 and free cash flow went negative, while significant claims recorded in contract assets and other non-current assets grew to roughly $680 million from about $400 million at the September 2025 fiscal year end. For STN, public budgets are the demand curve here, so a funding freeze, an election-driven pause or a slower federal appropriations cycle in the United States shows up as delayed starts and lower utilization.

Pick ACM if you believe its drivers more; STN if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the ACM and STN guides.

ACM. The valuation reflects skepticism about cash conversion, not about the order book. At roughly 12 times forward earnings and about 9.9 times EV/EBITDA, AECOM prices below an engineering and consulting peer group closer to 13 times, despite carrying higher margins than the peer average, a gap management has explicitly flagged in its investor slides. Trailing GAAP metrics look less flattering (net income of about $506 million on $16.0 billion of revenue is a 3.2% margin, giving a trailing P/E near 19.5), which is why the forward and trailing multiples tell such different stories. Return on equity near 29% and a share count down roughly 20% since 2020 are what the forward multiple is capitalizing.

STN. Stantec reports in Canadian dollars while trading in US dollars on the NYSE, so screener figures often mix currencies and should be checked against the company's own releases. The 2026 guide of ~8.5% to ~11.5% net revenue growth with ~17.6% to ~18.2% adjusted EBITDA margin was reaffirmed alongside Q1 results in May 2026. A ~23x trailing multiple against a 52-week range of roughly $66 to $114 shows most of the past year's move came from the multiple, not from the earnings line.

Headline figures (approximate, August 2026): ACM shows revenue (ttm) ~$16.0 billion, with net service revenue near $1.95 billion a quarter, fiscal 2026 guidance ~$5.90 to $6.10 adjusted EPS, ~$1.275 to $1.305 billion adjusted EBITDA, ~$400 million free cash flow, total backlog ~$26.2 billion, a record, up ~8% year over year, adjusted ebitda margin ~16.5% in fiscal Q2 2026, with Americas segment margin at ~20.0%; STN shows net revenue (fy2025) ~C$6.5 billion, up ~10.7%, adjusted ebitda (fy2025) ~C$1.14 billion, ~17.6% margin, q1 2026 adjusted eps ~C$1.33, up ~14.7%, contract backlog ~C$9.0 billion, up ~13.2% y/y.

ACM and STN are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined ACM and STN exposure against your real portfolio. It is not an investment adviser.