The news says the government has shut down. Then the mail arrives and Social Security payments land on schedule. So what actually closed? The answer runs through a calendar most people never see, and a law from 1870 that makes stopping the only legal option.
The Deadline Is Built Into the Calendar
The federal fiscal year runs from October 1 to September 30. Before it starts, Congress is supposed to pass 12 regular appropriations bills, one for each slice of the government: defense, agriculture, homeland security, and so on. Each bill hands its agencies the money they may spend that year.
That almost never happens on time. Since the current fiscal calendar took effect in 1977, Congress has finished all 12 bills before the deadline in exactly four years: 1977, 1989, 1995 and 1997. Since 1998, the last of a year's spending bills has arrived an average of about 117 days late.
The usual patch is a continuing resolution, or CR, a short bill that keeps agencies running near last year's funding for a few weeks or months. CRs are common because keeping things the same is easier to agree on. A shutdown is what happens when even the patch fails.
A lapse does not have to hit everything. If nine bills pass and three do not, only those agencies close. The longest lapse on record covered one department: Homeland Security went without appropriations from February 14 to April 30, 2026.
Authorization Is Not Appropriation
Congress funds things in two steps, and only the second one moves money.
An authorization is the law that creates an agency or program and says what it may do. It often sets a ceiling on spending, but it provides no money.
An appropriation grants budget authority, the legal permission for an agency to sign contracts and draw money from the Treasury. A program can be fully authorized and still have nothing to spend. When people say Congress failed to fund the government, they mean the second step.
Why Agencies Stop Instead of Running a Tab
A business short on cash can buy on credit and settle later. A federal agency cannot. The reason is the Antideficiency Act, which dates to 1870 and is still in force.
The law forbids an agency from spending, or promising to spend, money Congress has not provided. It also forbids accepting volunteer work as a way around that. A willful violation carries a fine of up to $5,000, up to two years in prison, or both.
One exception is large. Work may continue for emergencies involving the safety of human life or the protection of property. Air traffic controllers, federal law enforcement and active-duty troops stay on duty under it. Congress narrowed the exception in 1990 so it cannot cover routine functions whose pause would threaten nobody.
What Keeps Running and What Stops
Federal spending falls into two buckets, and only one sits on the annual calendar.
Mandatory spending flows from standing law and needs no yearly vote. Social Security, Medicare and Medicaid are the largest pieces, and those payments keep going during a lapse. Mandatory spending plus interest on the debt is roughly three quarters of the budget. Money going out is not the same as service being available, though. Benefits continue while some counter work, such as issuing a replacement card, stops.
Discretionary spending is what the 12 bills cover, about a quarter of the total, and it is the part that lapses. It pays for park rangers, food inspectors, museum staff, grant offices and research labs.
What you notice depends on choices agencies make. The Interior Department closed the national parks in October 2013. During the 2018 to 2019 shutdown many stayed open with almost no staff, and Joshua Tree National Park was left with vandalism, illegal off-roading and destroyed trees. Passports are a different case. That work is paid for by applicant fees rather than annual appropriations, so it continues, unless the office sits inside a federal building that closes.
Excepted, Exempt and Furloughed
Federal workers fall into three groups, and the labels sound alike.
Furloughed staff are sent home and told not to work. Working anyway would break the Antideficiency Act.
Excepted staff are paid from the annual bills, but their duties fall under the emergency exception. They report to work with no paycheck until funding returns.
Exempt staff are paid from another source, such as fees or multi-year funds, so they work and are paid on time.
The Government Employee Fair Treatment Act of 2019 guarantees back pay to federal employees, furloughed and excepted alike, as soon as possible after the lapse ends. Before that law, each shutdown's back pay took its own vote.
Contractors get no such guarantee. The person cleaning a closed federal building usually works for a private company holding a government contract, and those lost hours are often never repaid. Making contractors whole takes separate legislation, which Congress has generally not passed.
What It Costs the Economy
Shutdowns do real damage, and most of it is temporary.
The Congressional Budget Office studied the 35-day partial shutdown of December 22, 2018 to January 25, 2019. It put the lost output at about $11 billion across two quarters. Roughly $8 billion came back once workers received back pay and delayed activity resumed. About $3 billion never did.
The 2025 shutdown ran 43 days, from October 1 to November 12. Partway through, CBO projected that a lapse of that length would permanently cost billions of dollars and take a meaningful bite out of that quarter's growth, with part of it coming back the next quarter as delayed money moved.
The permanent piece is work that was never done. A closed lab does not run twice the experiments later to catch up.
A Shutdown Is Not a Debt Ceiling Standoff
People mix these two up constantly. They are different problems.
A shutdown is about spending authority. Congress has not said the money may be spent, so agencies cannot spend it.
The debt ceiling is about borrowing authority. It caps how much the Treasury may owe, and it applies to bills Congress has already run up. Hitting it closes no offices. It stops the Treasury from raising the cash to cover obligations that already exist.
They are not the same size of problem. A shutdown closes offices and delays paychecks that eventually arrive. Breaching the debt ceiling would put every federal payment at risk at once, including interest owed to everyone holding a Treasury bond.
