Compounding, Revisited

The standard compounding sermon goes something like this. Start early. Save consistently. Time in the market beats timing the market. Albert Einstein supposedly called compound interest the eighth wonder of the world. Over forty years at a seven percent real return, a dollar saved today becomes fifteen. Therefore, anyone who fails to retire wealthy has only themselves to blame.

The arithmetic is unassailable. The story is incomplete to the point of being misleading, particularly for the audience it most often gets delivered to.

What the chart conceals

The compounding chart is a deterministic curve drawn against time. What it conceals is the variance underneath, the assumptions baked into the constants, and the structural variables that determine whether any given person is actually able to ride the curve in the first place.

The first concealed variable is starting capital. A dollar compounding for forty years at seven percent becomes fifteen dollars. A million dollars compounding under identical assumptions becomes fifteen million. The difference isn't work ethic, isn't discipline, isn't virtue. It's starting position. The compounding chart treats this as a non-issue by assuming everyone has access to the same productive function. Empirically, the function is the same. The inputs are not.

The second concealed variable is liquidity. Compounding works arithmetically when you can leave the position alone for forty years. Most people in the bottom three quintiles of household wealth can't, because a medical event, a job loss, a family obligation, or a housing shock will arrive somewhere in the forty-year window and force a withdrawal at exactly the wrong time. The compounding story assumes the position is never touched. Real life routinely touches it.

The third concealed variable is the gap between expected and realised returns. The seven percent real return that anchors most compounding charts is a long-run average dragged through a particular period of US equity history. Real lived returns over any given thirty-year window have ranged from about three percent to about nine percent, and the path matters as much as the destination. A bad first decade can permanently impair the compounding effect, even if the average eventually recovers.

Piketty's claim, less politely stated

Thomas Piketty's r > g (return on capital exceeds economic growth) is usually framed as an observation about inequality. It's also a precise warning to anyone trying to build wealth through labour income alone. The return on capital structurally outpaces the rate at which wages grow. Compounding works much harder for someone whose dollars are already in the system than for someone trying to add new dollars to it from their salary.

The implication isn't that compounding is wrong. The implication is that the compounding strategy is fundamentally different depending on your starting position. For someone with capital, the strategy is to own. For someone without, the strategy is to acquire earning capacity that outpaces wage compression, then convert to ownership as fast as possible. The middle-class compounding narrative collapses these two strategies into one, which is what makes it incomplete when delivered to people without buffers.

What I still do

None of this is an argument against compounding. The arithmetic is correct. I run the same playbook anyone else does. Automated index allocation, time-in-market discipline, position sizing for sleep. The compounding sermon is wrong in what it omits, not in what it says.

What I've stopped doing is treating compounding as a moral story. The chart doesn't say anything about character. It says something about the function applied to a starting position over a specific time horizon under specific assumptions. The people who do well by it are mostly people who started with capital, never had to touch the position, and lived through a favourable return window. The people who do poorly are mostly people who experienced one or more of those variables breaking.

The honest version of the sermon is this. Compounding is real. The story is structural. Your starting position matters more than the financial press will tell you. Your liquidity buffer matters more than your contribution rate in the first decade. The chart is a tool, not a verdict. And (most usefully) the chart's logic applies to assets other than money. Compounding works on knowledge, on relationships, on systems, on professional reputation. The four-decade horizon is exactly the right frame. The variables you choose to compound across are the actual question.

That's the part the sermon never quite gets to.