Aon plc vs Marsh McLennan
Prices at close . Model readings .
Aon plc
$315.72+4.37%- Market value
- $67.25B
- P/E
- 15.9
- 1 year
- −5.8%
Marsh McLennan
$192.30+0.85%- Market value
- $92.11B
- P/E
- 19.3
- 1 year
- +4.1%
Price change, with the S&P 500 as a benchmark
Percent change in each close since the start of the chosen range, for both companies and the S&P 500 (SPY). Daily closes over the last year, weekly before that and monthly before five years.
How the two compare
On the latest closes (28 Oct 2026), Marsh McLennan is the larger company by market value ($92.11B against $67.25B). Over the past year Aon plc returned −5.8% and Marsh McLennan +4.1%, while the S&P 500 returned +12.7%. The latest filed P/E is 15.9 for Aon plc and 19.3 for Marsh McLennan, and the operating margin 19.7% against 17.7%. Over the next 21 sessions the model expects −0.65% for Aon plc, with a 12% chance of a rise, and −0.26% for Marsh McLennan, with a 44% chance. Aon plc's long-run fair value is $267.54, a gap of −15.3% to its price; the long-run model view is negative. Marsh McLennan's long-run fair value is $147.06, a gap of −23.5% to its price; the long-run model view is negative.
What the model expects
Expected returns and the chance of a rise from our forecasting models, and the long-run fair value against the price. Readings, not advice.
How the prices moved
Price change over each period, with the S&P 500 (SPY) for comparison.
What the market pays
Size and the multiples from the latest filed quarter. A P/E on losses reads n/m.
How much of revenue becomes profit
Margins and returns on capital from the latest filing; revenue, net income and earnings per share over the trailing twelve months.
How fast the business grew
Change against the same quarter a year earlier.
Balance sheet and quality scores
Leverage, liquidity and two published scores: Altman Z (below 1.8 the distress zone, above 3 the safe zone) and Piotroski F (0 to 9).
How the shares trade
Volatility, sensitivity to the market, the deepest fall, short interest and how closely the two move together.
Aon plc or Marsh McLennan: common questions
Which is larger by market value, Aon plc or Marsh McLennan?
Marsh McLennan, at $92.11B against $67.25B for Aon plc, on the latest closes (28 Oct 2026).
Which has the higher P/E ratio, Aon plc or Marsh McLennan?
Marsh McLennan has the higher latest filed P/E, 19.3; Aon plc's is 15.9. Filings: quarter to 30 Sep 2026.
How did Aon plc and Marsh McLennan move over the past year against the S&P 500?
Over the past year Aon plc returned −5.8% and Marsh McLennan +4.1%, while the S&P 500 returned +12.7%. Prices at close 28 Oct 2026.
What does the model expect for Aon plc and Marsh McLennan over the next month?
−0.65% for Aon plc with a 12% chance of a rise, and −0.26% for Marsh McLennan with a 44% chance, over the next 21 sessions. Model readings 28 Oct 2026. These are model readings, not advice.
How do the operating margins of Aon plc and Marsh McLennan compare?
The operating margin is 19.7% for Aon plc and 17.7% for Marsh McLennan. Filings: quarter to 30 Sep 2026.
Do Aon plc and Marsh McLennan shares move together?
Over the past year the correlation of their daily returns was 0.78 (often together); 1 means they always move together, 0 unrelated, −1 opposite. Prices at close 28 Oct 2026.
Model readings are research estimates, not investment advice. Prices: daily closes. Fundamentals: the latest SEC filings. Short interest: FINRA, settlement 30 Sep 2026. A dash means the figure is not in our data; it is never shown as zero. The model view follows a published rule: next month by the sign of the expected return, the long run positive at a fair value 10% or more above the price and negative at 10% or more below it.