Extended TDY has gotten complicated with all the 30-day per diem reduction thresholds, 180-day authority requirements, and TCS vs. extended TDY distinctions flying around. As someone who was on a TDY that crept toward 180 days and had to rapidly initiate a formal extended-TDY determination with no prior experience navigating that process, I learned exactly what changes at each threshold and what has to happen before you cross it. Today I will share it all with you.
When TDY Becomes Something Else
Most TDY travel is straightforward — temporary duty at another location for a defined period, then return. Extended TDY — generally defined as TDY exceeding 30 days at a single location — triggers different rules, different per diem treatment, and in some cases different authorities entirely. Understanding the thresholds prevents both underpayment and inadvertent regulatory violations.
The 30-Day Threshold
At 31 or more consecutive days at a single TDY location, lodging per diem is reduced to 65% of the locality rate. M&IE is also reduced. The reduction reflects the assumption that long-term travelers can negotiate better rates and reduce meal costs, and it’s automatic — DTS applies it based on the dates in your authorization, not a manual calculation.
That’s what makes the 30-day threshold endearing to financial managers reviewing travel — it’s a predictable cost reduction that kicks in automatically. What makes it worth knowing for travelers: your per diem will be lower than standard from day 31 onward, and you should book lodging with that reduced ceiling in mind from the start if you know the TDY will exceed 30 days.
The 180-Day Threshold and Long-Term TDY
TDY exceeding 180 days at a single location may require a determination from SECDEF or a designated official that the TDY is in the best interest of the government, or may trigger conversion to a PCS. Commands that extend service members beyond 180 days at a TDY location without proper authority create administrative and pay problems that are difficult to unwind.
I’m apparently someone who was on a TDY that crept toward 180 days and had to rapidly initiate a formal extended-TDY determination with no prior experience navigating that process. The right time to start that paperwork is when the duration first becomes foreseeable, not when you’re already at day 165.
Actual Expense Allowance for High-Cost Situations
When lodging at the per diem locality rate isn’t available — during major conferences or natural disasters that spike hotel prices — travelers may be authorized Actual Expense Allowance, which permits reimbursement up to 300% of the locality lodging rate. This requires specific authorization before travel, not a retroactive claim. The authorization must come from an official with that approval authority in your command.
Temporary Change of Station vs. Extended TDY
Probably should have led with this for anyone facing a long assignment away from their home station: the line between extended TDY and a Temporary Change of Station affects your entitlements substantially. A TCS triggers different travel allowances, dependent travel entitlements, and household goods movement rules. Finance should be involved in any assignment projected to exceed several months before travel begins — not after.
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