Every retirement plan, every health budget, and every family conversation about the spare room rests on one unexamined sentence: somebody will be there.

That was never a plan. It was an accident, a hundred-year overlap of large families, women outside the paid workforce, and a short old age. All three have now ended at once, and nobody has worked out what replaces them.

In 2010 there were seven Americans of caregiving age for every person over eighty. By 2050 there will be fewer than three. Thirty-eight million people already provide six hundred billion dollars a year of unpaid care that appears in no national account. The paid workforce meant to catch what families drop must fill 9.7 million job openings this decade at a median wage under twenty-six thousand dollars. And twenty-one million Americans will reach old age with no partner and no children at all.

The Care Deficit follows that arithmetic wherever it leads: into the daughter who quietly rearranges her career, the aide who leaves with a ruined back, the hospital bed occupied by someone with nowhere to go, the estate consumed in three years of nursing home fees. It goes to Japan, which arrived first and is still short half a million workers. It examines what care robots actually did when deployed at scale, and finds they increased employment by a quarter instead of reducing it.

The conclusion is uncomfortable and unavoidable. The shortfall cannot be closed by money, machines, migration, or higher birth rates. It can only be distributed. And a distribution nobody decides is not neutral: it falls on the oldest, the poorest, and the woman with the most interruptible job.

A clear-eyed account of the one part of a human life for which no society has yet made an honest arrangement, and of what it would take to make one.