# Other People's Money: How Insurance Float Built Berkshire Hathaway Warren Buffett built a $176 billion war chest out of money that is not his: insurance float, the premiums held before claims are paid. How it works, and what it echoes for everyone else. Author: J.A. Watte Published: July 4, 2026 Source: https://jwatte.com/blog/berkshire-insurance-float/ --- The single most important number in the story of the most admired investor of the last century is not his stock picks or his batting average. It is $176 billion of money that does not belong to him. That is the size of Berkshire Hathaway's insurance float at the end of 2025, and float is the quiet engine underneath the whole legend ([Berkshire Hathaway 2025 shareholder letter](https://www.berkshirehathaway.com/letters/2025ltr.pdf)). This series keeps finding the same structural advantage under institutions that hold money, the [insurance carriers that invest their premiums](/blog/runway-and-ruler/), the [university that built its own insurer](/blog/fiat-lux-uc-captive-insurance/). Warren Buffett did not discover that advantage, but he pressed it harder and longer than anyone alive, and he explained it more plainly. This is how float works, and what an ordinary person can see in it. ## What float is, in Buffett's own words Buffett has defined float in his shareholder letters more clearly than any textbook. "To begin with," he wrote in 1997, "float is money we hold but don't own. In an insurance operation, float arises because premiums are received before losses are paid, an interval that sometimes extends over many years" ([1997 letter](https://www.berkshirehathaway.com/letters/1997.html)). He put it even more simply in 2009: "Insurers receive premiums upfront and pay claims later. This collect-now, pay-later model leaves us holding large sums, money we call float, that will eventually go to others. Meanwhile, we get to invest this float for Berkshire's benefit" ([2009 letter](https://www.berkshirehathaway.com/letters/2009ltr.pdf)). That is the entire trick, and it is not a trick at all. When you buy an insurance policy, you pay first and the insurer pays your claim, if you ever have one, months or years later. In the gap, the insurer holds your money. Multiply that across millions of policies and the pile never empties, because new premiums come in as old claims go out. The insurer gets to invest the pile and keep what it earns. The money will eventually go to policyholders, but until it does, it works for the company holding it. ## From $8.6 million to $176 billion Buffett bought his way into that machine in early 1967, paying $8.6 million for a small Omaha insurer called National Indemnity ([2014 letter](https://www.berkshirehathaway.com/letters/2014ltr.pdf)). The float that came with it was tiny, around $16 to $20 million by his own accounts, but it was the seed of everything ([2009 letter](https://www.berkshirehathaway.com/letters/2009ltr.pdf); [2004 letter](https://www.berkshirehathaway.com/letters/2004ltr.pdf)). The growth from there is worth seeing as a single line, from Buffett's own table: $39 million in 1970, $237 million in 1980, $1.6 billion in 1990, $27.9 billion in 2000, $65.8 billion in 2010, and $91.6 billion in 2016 ([2016 letter](https://www.berkshirehathaway.com/letters/2016ltr.pdf)). It reached $171 billion at the end of 2024 and $176 billion at the end of 2025 ([2024 letter](https://www.berkshirehathaway.com/letters/2024ltr.pdf); [2025 letter](https://www.berkshirehathaway.com/letters/2025ltr.pdf)). Buffett once noted the compounding rate behind it: since 1967, the float grew at an annual rate of 21.7 percent ([1997 letter](https://www.berkshirehathaway.com/letters/1997.html)). It came from four engines. National Indemnity, the 1967 purchase, is the original and, Buffett says, "the largest property/casualty company in the world as measured by net worth" ([2016 letter](https://www.berkshirehathaway.com/letters/2016ltr.pdf)). GEICO, the car insurer Berkshire had owned a piece of since the 1970s, was bought outright on January 2, 1996, when Berkshire "acquired the remaining 50% of GEICO for $2.3 billion in cash" ([2009 letter](https://www.berkshirehathaway.com/letters/2009ltr.pdf)). General Reinsurance followed in 1998. And the largest single source is the Berkshire Hathaway Reinsurance Group, built by Ajit Jain, whom Buffett hired in the mid-1980s and about whom he wrote the line every Berkshire watcher knows: "If Charlie, I and Ajit are ever in a sinking boat, and you can only save one of us, swim to Ajit" ([2009 letter](https://www.berkshirehathaway.com/letters/2009ltr.pdf)). ## Why float is better than free Here is the part that separates a good idea from a fortune. Float is not automatically valuable, because the insurer might pay out more in claims than it collected in premiums, and then the float has a cost, the underwriting loss. Buffett's insight, and his discipline, was to insist on underwriting that at least broke even, which turns the float into free or better-than-free money. "Float is wonderful," he wrote in 2004, "if it doesn't come at a high price. Its cost is determined by underwriting results. When an underwriting profit is achieved, as has been the case at Berkshire in about half of the 38 years we have been in the insurance business, float is better than free. In such years, we are actually paid for holding other people's money" ([2004 letter](https://www.berkshirehathaway.com/letters/2004ltr.pdf)). Sit with that sentence, because it is the whole thing. In a good year, an insurance company is not borrowing money to invest. It is being paid to accept it. Buffett quantified it in that same letter: "last year we were paid more than $1.5 billion to hold an average of about $45.2 billion" ([2004 letter](https://www.berkshirehathaway.com/letters/2004ltr.pdf)). He described the effect elsewhere as if "someone deposited $62 billion with us that we could invest for our own benefit without the payment of interest" ([2009 letter](https://www.berkshirehathaway.com/letters/2009ltr.pdf)). Ordinary companies borrow at a cost and hope to earn more than that cost. Berkshire was handed leverage at a negative cost, decade after decade, and invested it. That is not a better hand at the same game. It is a different game. The reason it compounds rather than merely helping one year is that the float is permanent even though any single dollar of it is temporary. Buffett warns against reading it as an ordinary debt: "to think of float as a typical liability is a major mistake. It should instead be viewed as a revolving fund" ([2016 letter](https://www.berkshirehathaway.com/letters/2016ltr.pdf)). A bill you must pay next week cannot be invested for thirty years. A revolving fund that stays roughly full forever can be, and thirty years of investing an interest-free, ever-refilling pile is how you turn millions into hundreds of billions. ## The mill that became a giant The best proof of what float can do is what Berkshire was before it had any. "Berkshire was then a northern textile manufacturer mired in a terrible business," Buffett wrote of the company he took over in the 1960s ([2014 letter](https://www.berkshirehathaway.com/letters/2014ltr.pdf)). Its net worth had fallen from $55 million to $22 million by 1964, and it owed its bank $2.5 million. Buffett spent eighteen years struggling with the looms before giving up: "In 1985, I finally threw in the towel and closed the operation" ([2014 letter](https://www.berkshirehathaway.com/letters/2014ltr.pdf)). What saved the company was the pivot he had made almost twenty years earlier. "Since Berkshire purchased National Indemnity in 1967," he wrote, "property-casualty insurance has been our core business and the propellant of our growth. Insurance has provided a fountain of funds with which we've acquired the securities and businesses that now give us an ever-widening variety of earnings streams" ([2004 letter](https://www.berkshirehathaway.com/letters/2004ltr.pdf)). The result of running that fountain for six decades is a per-share value that compounded at 19.7 percent a year from 1965 to 2025, an overall gain the 2025 letter puts at 6,099,294 percent ([2025 letter](https://www.berkshirehathaway.com/letters/2025ltr.pdf)). A failing New England mill became one of the most valuable companies on earth, and the machine that did it was not stock picking alone. It was disciplined underwriting that produced float, plus decades of investing that float. Buffett stepped down as chief executive on January 1, 2026, and the 2025 letter, written in his successor Greg Abel's voice, summed up the life's work as "building a great insurance business since the acquisition of National Indemnity in 1967, and deploying the float to make successful investments" ([2025 letter](https://www.berkshirehathaway.com/letters/2025ltr.pdf); [CNBC](https://www.cnbc.com/2026/01/01/warren-buffett-retires-as-berkshire-hathaway-ceo.html)). ## What the rest of us can see in it You cannot buy National Indemnity. But the principle Buffett exploited is visible everywhere once you know its shape: whoever holds and invests other people's money in the gap between collecting it and paying it out keeps the earnings, and that is a structural edge no amount of cleverness on the other side can fully offset. It is why the [insurance industry is an investor first](/blog/runway-and-ruler/) and a claims-payer second, and why the [University of California built its own insurer](/blog/fiat-lux-uc-captive-insurance/) rather than keep renting one. There is a retail echo of it, and it is worth understanding without being sold on it. In permanent life insurance, whole or universal, the premium is deliberately set higher than the true cost of the insurance in the early years. The insurer holds and invests that excess, and it accumulates as policy cash value that grows tax-deferred, because the policyholder's premiums are being invested by the insurer just as Berkshire invests its float ([whole life insurance](https://en.wikipedia.org/wiki/Whole_life_insurance); [cash value](https://en.wikipedia.org/wiki/Cash_value)). That is a real mechanism, and it is the same mechanism at individual scale. But the honest version comes with Buffett's own caution attached. The advantage belongs to the disciplined holder of the float, not automatically to everyone who touches it. Buffett notes that insurers as a group "generally earned poor returns" because insurance is "a commodity-like product," and that float "can be drowned by poor underwriting results" ([2016 letter](https://www.berkshirehathaway.com/letters/2016ltr.pdf)). At the retail level that means the insurer keeps a spread, the fees and commissions are front-loaded, and the returns are modest. The lesson is not that a life policy makes you Warren Buffett. The lesson is the one Buffett spent sixty years demonstrating: the person who gets to hold and invest other people's money, cheaply and for a long time, has an advantage worth understanding, whichever side of the policy you are on. ## Related reading - [The Runway and the Ruler](/blog/runway-and-ruler/): the insurance float mechanism and the offshore towers it feeds. - [Let There Be Light, and a Reserve](/blog/fiat-lux-uc-captive-insurance/): the University of California building its own insurer to keep the float. - [The Hundred-Billion-Dollar Nonprofit Whose Profit Rides on the Market](/blog/kaiser-permanente-ledger/): another institution whose bottom line is set by its portfolio. - [The Working Ledgers](/blog/the-working-ledgers/): the market underneath every institution that holds money. ## Fact-check notes and sources - **Berkshire's float figures** (float of $176 billion at year-end 2025, up from $171 billion in 2024 and $91.6 billion in 2016, with the historical table of $39 million in 1970, $237 million in 1980, $1.6 billion in 1990, $27.9 billion in 2000, and $65.8 billion in 2010; the 21.7 percent compounding rate since 1967; and the four sources National Indemnity, GEICO, General Re, and Berkshire Hathaway Reinsurance): from Warren Buffett's Berkshire Hathaway shareholder letters, the [2025 letter](https://www.berkshirehathaway.com/letters/2025ltr.pdf), [2024](https://www.berkshirehathaway.com/letters/2024ltr.pdf), [2016](https://www.berkshirehathaway.com/letters/2016ltr.pdf), [2009](https://www.berkshirehathaway.com/letters/2009ltr.pdf), [2004](https://www.berkshirehathaway.com/letters/2004ltr.pdf), [2014](https://www.berkshirehathaway.com/letters/2014ltr.pdf), and [1997](https://www.berkshirehathaway.com/letters/1997.html). - **The definitions and the economics of float** (float as "money we hold but don't own," the "collect-now, pay-later" model, "better than free" and "paid for holding other people's money," the $1.5 billion paid to hold $45.2 billion, the "revolving fund" framing, and the "poor returns"/commodity caution): quoted verbatim from the [1997](https://www.berkshirehathaway.com/letters/1997.html), [2004](https://www.berkshirehathaway.com/letters/2004ltr.pdf), [2009](https://www.berkshirehathaway.com/letters/2009ltr.pdf), and [2016](https://www.berkshirehathaway.com/letters/2016ltr.pdf) letters. - **The National Indemnity purchase and the textile history** (the $8.6 million 1967 purchase; the fall in net worth from $55 million to $22 million by 1964; the 1985 closing of the textile operation; the 1996 GEICO purchase for $2.3 billion; and the Ajit Jain quotation): from the [2014](https://www.berkshirehathaway.com/letters/2014ltr.pdf), [2009](https://www.berkshirehathaway.com/letters/2009ltr.pdf), and [2004](https://www.berkshirehathaway.com/letters/2004ltr.pdf) letters. Buffett dates the Jain hire to the mid-1980s (his letters give both 1985 and 1986). - **The 19.7 percent compounding and the CEO transition** (Berkshire's per-share market value compounding 19.7 percent annually from 1965 to 2025; Buffett stepping down as CEO on January 1, 2026, while remaining chairman, with Greg Abel as CEO): [2025 letter](https://www.berkshirehathaway.com/letters/2025ltr.pdf) and [CNBC](https://www.cnbc.com/2026/01/01/warren-buffett-retires-as-berkshire-hathaway-ceo.html). - **The permanent-life-insurance echo** (that permanent life insurance premiums are invested by the insurer and accumulate as tax-deferred cash value, with fees and modest returns as the caveat): [Wikipedia, "Whole life insurance"](https://en.wikipedia.org/wiki/Whole_life_insurance) and ["Cash value"](https://en.wikipedia.org/wiki/Cash_value), presented as an analogy at the mechanism level, not a claim that a life policy replicates Berkshire's returns. *This post is informational and historical, not financial or investment advice. All figures are reproduced from the cited shareholder letters and public sources. Individuals and companies are discussed from the public record as nominative fair use, with no affiliation implied.* --- Canonical HTML: https://jwatte.com/blog/berkshire-insurance-float/ RSS: https://jwatte.com/feed.xml JSON Feed: https://jwatte.com/feed.json Hero image: https://jwatte.com/images/berkshire-insurance-float.webp