Insurance Float: The Berkshire Hathaway Model and Its Limits
Premiums collected before claims are paid can be invested — the float, which Warren Buffett built Berkshire Hathaway around, functioning as leverage at near-zero cost. It cannot become ever-cheaper premiums: regulators require the capital held as reserves, gains accrue to owners, claims inflate alongside returns (sustainable real withdrawal is 3–4%), and short-tail lines like home insurance generate little float.
Insurers collect premiums before they pay claims. The money held in the interval — reserves against claims incurred but not yet settled — is called the **float**, and it can be invested. This is the real profit engine of the insurance business, and the source of a persistent misconception about what it can do. ## The Berkshire model Warren Buffett built Berkshire Hathaway around exactly this insight: acquire insurers (GEICO, General Re, National Indemnity), underwrite at or near break-even to grow the float, and invest that float in equities and whole businesses. Float behaves like leverage with a negative or near-zero cost of borrowing — provided underwriting doesn't lose money. Over six decades this made Berkshire one of the most valuable companies in the world. It has proven to be an outstanding way to compound capital. ## Why it doesn't produce ever-cheaper insurance The intuition that an insurer could invest the float and hand the returns back as steadily falling premiums fails on four points: **Regulators require the capital to be held.** Solvency rules force insurers to maintain reserves and capital against outstanding liabilities. Investment gains largely accrue to that capital base; they cannot be paid out as an ever-shrinking premium. **The gains belong to the owners.** In a stock insurer, returns go to shareholders. In a mutual, they can return to members — and mutuals do exactly this, which is why their premiums run modestly cheaper rather than approaching free. See Mutual Insurance and the Assessable Mutual. **Claims inflate too.** Rebuild costs at minimum track construction inflation, so much of a nominal return is consumed keeping pace with the liability. Sustainable real withdrawal is on the order of 3–4%, not the headline nominal return. **Float is small in short-tail lines.** Home and auto claims settle in months. The large, long-lived floats are in long-tail liability lines where claims settle over years or decades. Home insurance simply does not generate much float per premium dollar. ## The endowment version A related proposal is to overfund early and let compounding eventually cover claims forever. The arithmetic is unforgiving: at roughly $1,000 a year of expected claims and a sustainable ~3.5% real withdrawal, funding one house in perpetuity requires around $28,000 of untouched principal. Accumulating that by overpaying takes about two decades — at which point you have built a savings account with extra steps, and the surplus can be either reserves or a refund, never both. The best capital allocator of the era ran this model for sixty years. The result was an enormous investment company, not free insurance. Related: Combined Ratio: Where an Insurance Premium Actually Goes.