The federal program. Phased retirement for federal employees sits in 5 U.S.C. §8336a for CSRS and §8412a for FERS, both captioned "Phased retirement," with regulations at 5 CFR part 831 subpart Q and 5 CFR part 848. The authority came from §100121 of MAP-21, Public Law 112-141, signed on 2012-07-06: a citable oddity, since the authorising statute is a highway-funding act. The Office of Personnel Management published final regulations on 2014-08-08, effective 2014-11-06. The design is a 50% schedule: the participant works half-time, receives about half their salary and about half the annuity they would otherwise be paid, generally must mentor other employees (the Postal Service is excepted), must have been employed full-time for the preceding three years, and must already be eligible for immediate retirement. Crucially it is not an entitlement — the employing agency must approve entry. Take-up has stayed very small relative to the federal workforce; a count published in August 2023 put participation at roughly a thousand employees government-wide.
Why the private sector stays informal. The reason is legal rather than inertia, which is worth knowing because it explains what a reader can actually negotiate. The Government Accountability Office found that 71% of large employers agreed that regulatory complexities and ambiguities involving federal tax and age-discrimination laws affect their ability to offer phased retirement programs. A formal program that selects participants by age invites scrutiny under age-discrimination law, so employers overwhelmingly prefer to handle requests case by case. The same research found roughly 5% of employers had a formal program against about 11% permitting it informally — informal is about twice as common as formal. And there is a striking gap between intention and outcome: around a quarter of workers aged 61 to 66 planned to reduce their hours, while under 15% later reported having been partly or gradually retired from their career job.
Drawing a pension while still working. Before 2007 a pension plan generally could not pay benefits to an employee who had not separated, which structurally blocked the "half-retire and top up from the pension" design. The Pension Protection Act of 2006 added IRC §401(a)(36), providing that a pension plan does not fail to be qualified solely because it permits distributions to employees who have attained a specified age and are not separated from employment: effective for plan years beginning after 2006, so the operative year is 2007. The Bipartisan American Miners Act of 2019 §104 then lowered that age from 62 to 59½ for plan years beginning after 2019. Two limits matter: the provision is permissive rather than mandatory, so the plan must choose to allow it, and it addresses pension and defined benefit plans; it is not a general statement about 401(k) in-service withdrawal rules.
What reduced hours can quietly cost. Health coverage is the first question, because employer plans condition eligibility on an hours threshold and dropping below it ends coverage, which matters most before Medicare eligibility at 65. Defined benefit accrual is the second and least understood: a plan whose formula uses the final few years of pay can produce a smaller benefit after phasing than before it, even with extra service credited. Beyond that, employer contributions and matching in a defined contribution plan are set as a percentage of pay, so they fall with it; someone already claiming Social Security below full retirement age meets the retirement earnings test; and the decision to stop outright instead is early retirement. One thing phasing definitely does not do is open the rule of 55: staying with the same employer on fewer hours is not a separation from service, so that exception never comes into play.