This is general education, not investment advice. The figures use the US system; many countries have equivalent accounts.

The quiet flip

Individual retirement accounts (IRAs) now hold roughly $19 trillion, well ahead of the about $10 trillion in 401(k) plans, according to the Investment Company Institute, the fund industry's data body. That's a notable reversal: IRAs are now the single largest store of US retirement savings. And it isn't because people love IRAs — it's because of what happens when they leave a job. A large share of IRA money arrives as a rollover from a former employer's 401(k), and the ICI finds a majority of traditional-IRA households hold such rolled-over money.

IRA vs. 401(k), in plain terms

A 401(k) is a retirement plan your employer sets up: you contribute from your paycheck (often with a company match), and the employer picks the menu of investments. An IRA is one you open yourself at a brokerage like Vanguard, Fidelity or Schwab — you control it, and you choose what it's invested in (or whether it's invested at all). Each comes in two tax flavors: traditional (you get a tax break now, pay tax on withdrawals later) and Roth (you pay tax now, withdrawals are tax-free later).

The trap: money that never gets invested

Here's the problem the data keep surfacing. When you roll a 401(k) into an IRA, your old plan usually sells your investments and sends the money as cash. It then sits in a cash or money-market position inside the IRA — earning very little — until you take a second step and actually buy investments. Many people never take that step, or forget the account exists.

Vanguard's research found that a large majority of savers who left rollover money in cash didn't even realize it was sitting uninvested — a phenomenon it calls "cash drag." The cost compounds quietly: cash might earn around 4% a year today, while a broad stock-market fund has historically returned roughly 10% a year on average over the long run. Across the years a rollover can sit forgotten, that gap adds up to real money left on the table — without the saver ever making a decision.

What to actually do

  • Check what you're holding. Log into every old account — 401(k)s from past jobs, any IRAs — and look at what each is invested in. If you see "cash" or "money market," that's the signal to act.
  • Pick an investment. If choosing feels paralyzing, a target-date fund matched to roughly when you'll retire is a sensible, diversified default that rebalances itself over time.
  • Mind the fees. Costs vary by provider; many brokerages now charge little or nothing to hold an IRA, so it's worth comparing.
  • Consolidate. Scattering money across several old 401(k)s and IRAs makes it easy to lose track. Combining them into one IRA makes it simpler to monitor and rebalance.
  • Know the tax angle. Rolling a traditional 401(k) into a traditional IRA is generally tax-free; rolling it into a Roth IRA triggers a tax bill that year on the converted amount, so plan for it.

The takeaway

The rise of the IRA is, on paper, a good-news story: it means Americans are accumulating large retirement balances. But an IRA is only as powerful as what's inside it. The single most valuable thing many savers can do is unglamorous — log in, find any cash that's quietly sitting out of the market, and put it to work. The money is already yours; the only question is whether it's actually invested.