A military temporary duty assignment can last anywhere from a single day to 180 consecutive days at one location, and how long any particular TDY runs depends on the mission, the funding available, and what the authorizing official approves. The Joint Travel Regulations treat 180 consecutive days as the ceiling for a standard TDY; going past that requires written approval from a high-level authority before travel begins. Most assignments come in well under that cap.
Typical Lengths by Mission Type
Within the 180-day window, duration tracks the purpose of the trip. A conference or single meeting may run a day or two. Operational support for a joint exercise or a disaster response often lasts one to several weeks. Specialized training, audits, and project work that calls for particular expertise can stretch to several months.
Funding is often the real constraint. Even when the mission itself could justify 120 days on the ground, an authorizing official may only approve 60 if that’s what the budget will cover. Service branch matters too. The Army, Navy, Air Force, and Marine Corps each layer their own internal guidance on top of the JTR, so approval workflows, documentation, and typical assignment lengths vary from one service to another.
The 180-Day Cap and What Happens if You Cross It
Under the JTR, a TDY at one location cannot exceed 180 consecutive days unless a higher authority specifically approves the extension in writing before travel begins.1The Joint Travel Regulations (JTR). Joint Travel Regulations – Table 1-6, Time Limits for Travel Orders The written request must justify why the assignment needs to run longer. If no one secures that approval and the traveler crosses into day 181, per diem stops. The traveler is still on orders, still working, but no longer receiving a daily allowance.
The JTR also blocks a common workaround: issuing a TDY order for 180 days or fewer, bringing the traveler home briefly, then sending them straight back to the same location. If the known or reasonably anticipated duration exceeded 180 days when the initial order was written, that sequence violates the rule regardless of any break in the middle.2The Joint Travel Regulations (JTR). Joint Travel Regulations – Section: Violation of 180-Day Rule
One clarification worth keeping in mind: for active-duty service members, exceeding 180 consecutive days without authorization does not automatically convert the TDY into a Permanent Change of Station. The assignment doesn’t reclassify itself. Per diem simply ends.
Training Assignments Use a Shorter Threshold
If your TDY is a course of instruction at a school or military installation, the JTR applies a different cutoff. Courses scheduled for 139 days or fewer (less than 20 weeks) are treated as TDY. Courses scheduled for 140 days or more are classified as a PCS from the start, and the school location becomes your permanent duty station.3The Joint Travel Regulations (JTR). Joint Travel Regulations – Section 032201, Courses of Instruction at a School or Installation
This distinction catches people off guard. If additional instruction pushes a course from under 20 weeks to 20 weeks or more at the same location, and the remaining time on the original order plus the extension equals 139 or more days, the assignment converts to a PCS. Entitlements, housing arrangements, and family relocation eligibility all shift with that change.
Reservists Face Automatic PCS Conversion at 181 Days
Reserve and National Guard members called to active duty face a stricter version of the 180-day rule. For a reservist who does not commute daily, a TDY of 180 days or fewer at one location entitles them to standard TDY allowances. Once the assignment hits 181 or more consecutive days, it automatically becomes a PCS and per diem stops entirely.4Defense Finance and Accounting Service. Reserve Normal (Business/Regular) TDY If original orders are amended to extend the TDY past 180 days, the TDY location becomes the permanent duty station from the date of the amended orders.
Civilian Federal Employees Have Their Own Length Rules
Civilian federal employees travel under the Federal Travel Regulation rather than the JTR, though the 180-day boundary still shapes the analysis. When a civilian TDY will last between six months and 30 months, the authorizing official has to determine before travel begins whether the assignment is genuinely temporary or should be classified as a PCS. If the assignment is temporary, the official then decides whether it should remain TDY or become a Temporary Change of Station.5The Joint Travel Regulations (JTR). Joint Travel Regulations – Section: Civilian Employees TDY Between 6 Months and 30 Months
Civilian employees on extended TDY also face a tax consequence military members do not. When a TDY assignment exceeds one year, all travel expense allowances, reimbursements, and direct government payments made on the employee’s behalf become taxable income, retroactive to the date the assignment was recognized as exceeding the one-year mark. The agency reimburses the employee for substantially all of the resulting income taxes through a Withholding Tax Allowance and an Extended TDY Tax Reimbursement Allowance.6eCFR. 41 CFR Part 301-11 – Subsistence Expenses – Section 301-11.602
Per Diem Shrinks the Longer You Stay
Even within the 180-day window, the percentage of per diem you receive drops as the assignment stretches out. For the first 30 days of a TDY, you receive the full locality per diem rate. From day 31 through day 180, the JTR switches to a flat-rate method at 75 percent of the locality rate. If your TDY has been authorized beyond 180 days, the flat rate drops further to 55 percent. The assumption is that a longer stay lets you find cheaper meals and negotiate extended-stay lodging rates, so costs decrease.
Extending a TDY Past 180 Days
Getting an extension approved is possible but requires authorization from a level well above the immediate chain. The JTR spells out the approval authority in Table 1-7, and for most service members that means the Secretary of the service concerned, or the Combatant Commander or Deputy Combatant Commander. No further delegation is authorized for most branches.7The Joint Travel Regulations (JTR). Joint Travel Regulations – Table 1-7, Authorizing and Approval Authority for TDY of 181 or More Consecutive Days The Army has a narrow exception for members assigned to a Warrior in Transition Unit, where a two-star flag officer or civilian equivalent may authorize the extension after a recommendation from U.S. Army Medical Command.
Bona fide extensions past 180 days can be authorized only when they result from unforeseen changes or delays. The request must be in writing and submitted before the extension takes effect whenever possible. If the mission doesn’t allow for advance authorization, the travel order can be issued and the request submitted immediately afterward. The approving authority then decides whether to approve the order as written, end the duty and return the traveler, convert the assignment to a PCS, shorten it to 180 days, or (for civilians) convert it to a Temporary Change of Station.8The Joint Travel Regulations (JTR). Joint Travel Regulations – Section: TDY Travel Authorization or Order Issued Before Request to Exceed 180 Days
Family Separation Allowance Starts at 30 Days
Service members with dependents who are sent on TDY for more than 30 continuous days may qualify for Family Separation Allowance, provided the dependents do not reside at or near the temporary duty location. If you can commute daily to where your dependents live, you’re considered to be at or near the TDY location and the allowance doesn’t apply.9Department of Defense. DoDI 1340.24 – Family Separation Allowance FSA is a monthly payment separate from per diem, meant to offset the added household costs of maintaining two locations.