The 4% Rule and Its Limits

About 4% of the starting pot, then rising with inflation, has historically lasted thirty years — as a guide, not a guarantee. (William Bengen; the Trinity study.)

The most quoted rule for turning a pot into an income is the "4% rule": withdraw 4% of your savings in the first year, then increase that dollar amount with inflation each year after. In US historical data — William Bengen's 1994 work, and the later Trinity study — a balanced portfolio drawn this way survived thirty years in almost every period tested.

It is a sound starting point, but only that. Three limits matter. It rests on US market history, which was unusually strong; many other markets did worse. It assumes a fixed thirty-year horizon and rigid spending. And it ignores fees and taxes. Lower future returns, a longer life, or high costs can make 4% too generous; genuine flexibility can make a higher rate safe.

The deeper lesson is that the withdrawal rate matters more than squeezing an extra point of return from markets. Drawing too much, too fast is the surest way to exhaust a pot — whatever shares and bonds happen to do.

Illustrative example: how fast the pot drains

The chart shows, illustratively, how a pot's likely lifespan shortens as the starting withdrawal rate climbs. Treat 4% as a conversation-starter you revisit as circumstances change — not a number to set once and forget.