Aon is a professional services firm that earns money by helping companies handle risk and people decisions. When a business needs insurance, Aon figures out what coverage it needs, finds the right insurer, and earns a commission on the premium paid. When a company needs to manage employee benefits or retirement plans, Aon advises on that too and charges fees for its consulting work. Revenue comes from two segments: Risk Capital, which brought in $11.3 billion in 2025, and Human Capital, which added $5.9 billion. Neither segment sells insurance directly. Aon sits in the middle, connecting clients to insurers and charging for that expertise. The diagram below traces where the money goes.
How Aon Makes Money
flowchart TD
A["Clients Across 120 Countries"] --> B["Risk Capital Services
11.3B revenue"]
A --> C["Human Capital Services
5.9B revenue"]
B --> D["Commissions & Fees
From Insurance Carriers"]
C --> E["Consulting & Advisory Fees
From Client Engagement"]
D --> F["Total Revenue
17.2B annually"]
E --> F
F --> G["Operating Cash Flow
3.5B generated"]
G --> H["Data, Analytics & Tech
Investment Loop"]
H --> I["Competitive Advantage
Retain & Attract Clients"]
I --> A
B --> J["Global Reach
London, Bermuda, Singapore"]
C --> J
J --> I
G --> K["Shareholder Returns
Dividends & Buybacks"]
K --> A
Five years of financial data tell a clear story of consistent growth with one notable disruption. Revenue climbed from $12.2 billion in 2021 to $17.2 billion in 2025, a 41% increase over the period. Organic revenue growth, which strips out acquisitions and currency swings, held at 6% in both 2024 and 2025. That kind of steady organic growth is meaningful because it suggests clients are staying and new business is coming in, not just that Aon bought its way to bigger numbers.
Aon Total Revenue, 2021 to 2025
Revenue in billions of US dollars. The jump from 2023 to 2024 reflects the acquisition of NFP, a benefits and insurance brokerage firm.
Free cash flow, which is the cash left after paying for operations and equipment, also grew over the period, from $2.0 billion in 2021 to $3.2 billion in 2025. One year stands out: free cash flow dipped to $2.8 billion in 2024, the same year Aon spent heavily to acquire NFP. That acquisition drove revenue higher but also pushed net debt from $10.4 billion in 2023 to $15.9 billion in 2024. By the end of 2025, net debt had pulled back to $14.1 billion, partly helped by the sale of the NFP Wealth business, which generated a $1.2 billion gain.
$15.2B
Total debt outstanding as of the most recent filing period
That debt load is one of the most important numbers in this story. Aon must maintain specific financial ratios to comply with the rules attached to its credit agreements. If those ratios slip, borrowing costs could rise and access to new capital could tighten. With $815 million in interest expense paid in 2025 alone, debt servicing already consumes a meaningful share of operating income.
2024
milestone
The NFP Acquisition Changes the Scale of the Business
Aon closed its acquisition of NFP, a benefits brokerage and consulting firm, in 2024. The deal added significant Human Capital revenue and pushed total revenue past $15 billion for the first time. It also added billions in debt and created integration costs that ran through both 2024 and 2025. By late 2025, Aon had sold off the NFP Wealth business for a large gain, suggesting it is still reshaping what it actually wants to keep from the deal.
The operating margin improved to 25.3% in 2025 from 24.4% in 2024. The adjusted operating margin, which strips out restructuring charges and acquisition costs, reached 32.4% in 2025, up from 31.5% in 2024. Part of that improvement came from a restructuring program called Accelerating Aon United, which Aon says delivered $160 million of net savings in 2025. That program is still running and cost $365 million in charges during the year.
$3.2B
Free cash flow in 2025, up 14% from $2.8 billion in 2024
What Is an Insurance Broker, and Why Does It Matter Here?
An insurance broker does not take on risk itself. It connects businesses that need coverage with insurers willing to provide it, and earns a commission based on the premium paid. This means Aon's revenue is tied to insurance premium levels and the volume of policies placed. If clients find ways to avoid traditional insurance, Aon's commission income shrinks even if overall risk in the world stays high.
The business model risk that Aon itself names in its filings is direct and specific. A growing number of clients are choosing to self-insure, use captive insurers they control themselves, or turn to capital markets instead of buying traditional insurance policies. At the same time, technology-enabled competitors are building tools that let companies place insurance without a broker at all. Aon earns most of its revenue from commissions tied to premiums, so any shift away from traditional insurance placements hits the core revenue engine.
What Is the OECD Pillar Two Tax?
Pillar Two is a global agreement that sets a minimum 15% tax rate on corporate profits, regardless of where a company is headquartered. Ireland, the UK, Singapore, and many European Union countries have already passed laws to implement it. Because Aon is incorporated in Ireland and earns income across many countries, this rule could increase how much tax it pays. The exact impact is still uncertain because the rules keep changing.
A second documented risk sits on the tax line. Because Aon operates in more than 120 countries, its tax planning has historically taken advantage of different national rates. The OECD Pillar Two global minimum tax, now enacted in several key jurisdictions where Aon operates, creates meaningful uncertainty about future tax costs. Aon says in its filing that it is actively monitoring the situation and has not yet determined the full financial impact.
A third risk is legal rather than structural. Aon faces claims from clients who allege they suffered losses because of incorrect insurance placements or poor consulting advice. These are called errors and omissions claims. Aon's filing notes that some past claims have already exhausted its own insurance coverage, meaning Aon paid those costs out of its own pocket rather than having an insurer cover them.
1%
Revenue from Aon's single largest client in 2025, showing how spread out the client base is
Aon serves clients in more than 120 countries, and its largest single client accounts for only about 1% of total revenue. That kind of diversification means no single client walking away would cause serious damage to the overall business.
The Bet
Aon's revenue model holds together only if companies keep relying on traditional insurance brokers to place coverage and manage risk. The whole organic growth story, the commission income, and the adjusted margin expansion all depend on that assumption staying true. If more clients shift to self-insurance, captive structures, or technology platforms that cut out the broker, the volume of premiums flowing through Aon shrinks and commissions fall with it. Aon is investing in data, analytics, and artificial intelligence to make itself harder to bypass, but whether those tools are enough to stay relevant against both traditional rivals like Marsh McLennan and Willis Towers Watson and newer technology-first competitors is still an open question.
Open question
Aon grew revenue 41% over five years, generates over $3 billion in free cash flow annually, and serves clients across more than 120 countries with no single client accounting for more than 1% of revenue. But it carries $15.2 billion in total debt, faces a business model that clients are actively trying to route around, and operates in a tax environment that is still being rewritten. Can Aon use its scale, data capabilities, and restructuring savings to stay indispensable to clients fast enough to offset the long-term pull toward self-insurance and technology-enabled alternatives, all while servicing a debt load that leaves limited room for error?
Compiled · 10-K · FY2025
