What the rule actually says. Ordinarily, withdrawals from a 401(k) before 59½ carry a 10% penalty. The Rule of 55 (an IRS provision, sometimes called the "separation from service" exception) waives that penalty on distributions from the plan of the employer you separate from, as long as the separation happens in or after the year you reach age 55. You still owe ordinary income tax — the rule removes only the penalty. Timing is by calendar year: if you turn 55 at any point in the year you leave, you qualify, even if you actually separate in, say, March before your birthday.
Why it's easier than 72(t). Compared to the Rule of 72(t) (Chapter 24), the Rule of 55 is dramatically less rigid. There's no required payment schedule, no locked five-year commitment, and no "busting" penalty for taking the wrong amount. You simply withdraw from the plan as needed — a lump sum, occasional draws, or a steady stream, whatever your plan permits. That flexibility makes it the preferred bridge for people who retire (or are laid off) at 55 or later and have a workplace plan to draw on.
The critical limitations. Three constraints define the rule, and missing any one is costly: 1. Only the most-recent employer's plan. The exception applies to the 401(k)/403(b) of the job you just left. Old 401(k)s from prior employers don't qualify — unless you first roll them into your current plan while still employed (if the plan allows), consolidating them under the qualifying plan before you separate. 2. Not IRAs — while they stay IRAs. An IRA is never itself eligible for the Rule of 55. But you can flip that: rolling pre-tax IRA money into your workplace plan before you separate converts it into 401(k) money that does qualify (see "Reverse rollover" below). This is the big one to get right in both directions. 3. Your plan must permit partial/flexible withdrawals. Some employer plans force a full lump-sum distribution rather than allowing periodic withdrawals after separation. Check your plan's rules before you rely on this.
The rollover trap. The single most common and expensive mistake: separating from service at 55+, then rolling the 401(k) into an IRA (a natural-seeming move for more investment choices and lower fees) — which forfeits the Rule of 55, because the money is now in an IRA. If you'll need penalty-free access between 55 and 59½, leave the money in the 401(k) until you're past 59½, then roll it over. Consider a partial approach: keep enough in the 401(k) to fund your bridge years and roll the rest to an IRA if you prefer.
The reverse rollover — enlarging the bridge. The trap runs one way; you can also run it deliberately in reverse. Because only money inside the qualifying plan is accessible under the Rule of 55, you can widen your penalty-free bridge by rolling other pre-tax retirement money into that 401(k) before you separate: old 401(k)s from prior jobs and pre-tax (traditional) IRAs alike. Once inside the plan, those dollars inherit the Rule-of-55 treatment. Four conditions apply: (1) your plan must accept incoming rollovers — many do, but not all; (2) only pre-tax money works — Roth IRAs can't be rolled into a 401(k) at all, and after-tax IRA basis generally can't either; (3) a SIMPLE IRA can only be rolled in after two years of participation; and (4) do it while still employed, before you separate — the safe path, since a plan may not accept roll-ins once you're a former employee. The trade-off: money you move into the 401(k) gives up the IRA's wider investment menu and (for IRAs) the ability to do Roth conversions from it, so only move what you actually expect to spend before 59½.
The public-safety head start. Qualified public-safety employees — police officers, firefighters, EMTs/paramedics, air-traffic controllers, certain federal law-enforcement and customs personnel — get the exception at age 50 (or after 25 years of service under the plan, per SECURE 2.0 enhancements) rather than 55, reflecting the earlier retirement norms in those careers.
Keeping the 401(k) as a bridge
An engineer is laid off in the year she turns 56. She has $700,000 in her current employer's 401(k) and $200,000 in an old IRA. Under the Rule of 55, she can pull from the $700,000 401(k) penalty-free (paying only income tax) to fund the years until 59½ — taking flexible amounts as needed. Her instinct is to roll the whole 401(k) to an IRA for better funds; if she does, she loses penalty-free access and would have to fall back on a rigid 72(t). Instead she leaves the 401(k) in place as her bridge, taps it as needed to 59½, and rolls it to an IRA afterward. Had she foreseen the layoff, she could have gone further: rolling the $200,000 pre-tax IRA into the 401(k) while still employed — assuming the plan accepts roll-ins — would have brought that money under the Rule of 55 too, turning a $700K bridge into a $900K one.