MIR vs TMO: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of September 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.

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. MIR and TMO 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 MIR and TMO 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.

Mirion Technologies (NYSE: MIR) designs and sells radiation detection, measurement, analysis and monitoring products across two segments: Nuclear & Safety, which serves nuclear power plants, defense, research labs and industrial customers, and Medical, which supports cancer-care delivery, medical diagnostics and practitioner radiation safety. The company came public through a 2021 SPAC merger and describes itself as the only pure-play public company of its scale in radiation measurement, giving investors combined exposure to the nuclear energy revival and advanced medical applications. Much of its value sits in a large installed base of equipment, dosimetry services and recurring aftermarket revenue.

Full MIR guide

Thermo Fisher Scientific, headquartered in Waltham, Massachusetts, is a global provider of scientific instruments, consumables, reagents, and services used across pharmaceutical and biotech drug development, clinical diagnostics, academic research, and environmental and industrial testing. The company operates through four reportable segments: Life Sciences Solutions (reagents, proteins, and consumables for research and bioproduction), Analytical Instruments (mass spectrometers, chromatography systems, electron microscopes, and laboratory equipment), Specialty Diagnostics (clinical diagnostic kits and transplant diagnostics), and Laboratory Products and Biopharma Services (supply-chain distribution, contract research through PPD, and contract drug manufacturing through Patheon). Revenue is generated through instrument sales, high-margin consumables and reagents that customers repurchase continuously, long-term service contracts, and growing contract development and manufacturing (CDMO) fees; consumables and services collectively account for a majority of annual sales and provide durable recurring revenue.

Full TMO guide

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

• MIR drivers: Nuclear power tailwind; Backlog and recurring revenue.
• TMO drivers: Bioprocessing and Biologic Drug Manufacturing Tailwind; Recurring Consumables and Reagents Engine.

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: Mirion has a history of GAAP net losses, and reported earnings remain thin relative to its valuation, so much of the story depends on adjusted figures. For TMO, the most significant near-term risk is a contraction in research funding from government agencies (including NIH) and from biotech companies whose access to capital markets has historically been cyclical; when funding tightens, customers delay instrument purchases and reduce consumable orders, pressuring organic revenue growth.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick MIR if you believe its drivers more; TMO 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 MIR and TMO guides.

MIR. Mirion trades as a growth-oriented industrial where adjusted EBITDA and free cash flow, not GAAP EPS, anchor most valuation work given ongoing net losses and heavy interest costs. Backlog above $1.1 billion and double-digit order growth support the multiple, but roughly $1.2 billion of debt keeps leverage in focus. Reported figures vary by source and date, so confirm current numbers before relying on them.

TMO. Thermo Fisher's trailing price-to-earnings ratio of roughly 26x sits approximately 18% below its own ten-year historical average of about 32x, reflecting a period of softer organic growth as the post-pandemic diagnostics and COVID-related revenue tailwind has faded. The adjusted operating margin of 22.7% for 2025 and management guidance for 6 to 8 percent adjusted EPS growth in 2026 suggest the earnings recovery is progressing, though the pace of organic revenue acceleration remains a key variable the market is watching. Free cash flow of roughly $6.3 billion gives the company significant flexibility for continued share repurchases, dividends, and acquisitions.

Headline figures (approximate, JULY 2026): MIR shows revenue (fy2025) ~$925M, revenue (q1 2026) ~$258M (+27.5% YoY), 2026 rev growth guidance ~22% to 24%, 2026 adj. ebitda guidance ~$285M to $300M; TMO shows revenue (full year 2025) ~$44.6 billion, revenue guidance (full year 2026) ~$46.3 to $47.2 billion, adjusted operating income (full year 2025) ~$10.1 billion, adjusted operating margin (full year 2025) ~22.7%.

MIR and TMO 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 MIR and TMO exposure against your real portfolio. It is not an investment adviser.