Planning for a horizon you can't see the end of

Life expectancy figures describe averages across populations. Planning to an average means roughly half the outcomes exceed it, which is an unusual standard to apply to money that must not run out.

For a couple, the relevant figure is longer still, because the plan generally has to support whichever spouse lives longer.

Over spans that long, inflation stops being a footnote. Even a modest rate meaningfully reduces purchasing power across three decades, and it compounds against every fixed income source in the plan.

The combination — an uncertain horizon and a certain erosion — is why planning conventions lean toward a longer assumption than the average suggests.