TDY Per Diem Calculator

Introduction to TDY lodging and M&IE estimates

A temporary duty travel estimate normally has two major parts. Lodging is generally reimbursed from the traveler’s documented hotel cost up to an authorized nightly limit. Meals & incidental expenses (M&IE) are generally based on a daily locality rate rather than the exact amount spent on food. Because those two components follow different rules, simply multiplying one daily figure by the trip length can produce a misleading total.

This TDY per diem calculator separates the components and applies a common domestic planning model. It assumes one destination and one rate pair for the whole trip. The number of lodging nights is one less than the number of travel days, while M&IE is paid at 75% on the departure and return days and at 100% on intervening days. The result is useful for budgeting, comparing destinations, and checking the rough scale of a travel authorization.

The built-in Washington, San Diego, and Fort Liberty figures are illustrative sample rates, not live government data. Official rates can change by locality, month, organization, and travel category. For a decision that affects an authorization or voucher, verify the applicable rate and use the custom option.

How to use the TDY per diem form

Select a sample destination or choose Custom to enter an official lodging ceiling and M&IE rate. Enter the total number of calendar days in travel status, including departure and return. For example, leaving Monday and returning Thursday is a four-day trip with three assumed lodging nights. Select Calculate Per Diem to produce a lodging subtotal, M&IE subtotal, and combined planning estimate.

The custom lodging field should contain a nightly amount, while custom M&IE should contain a daily amount. Both inputs use dollars and cents and may be zero when an applicable allowance is unavailable. Travel days must be a whole number from 1 through 365. The calculator does not ask for nights separately because it assumes nights equal days minus one.

1. Confirm the destination and dates covered by the same locality rate.
2. Enter all travel-status days, not only full workdays at the duty site.
3. Review lodging and M&IE separately before relying on the combined total.
4. Use Copy Summary to move the result into a planning note or worksheet.

The formulas for TDY nights, travel days, and total per diem

Let L represent the nightly lodging rate, M the full daily M&IE rate, and d the number of travel days. The calculator first derives lodging nights N and full-rate middle days F. It then calculates the M&IE subtotal R and total estimate T.

A one-day trip therefore has no lodging and one reduced M&IE day. A two-day trip has one night and two reduced M&IE days. From the third day onward, each additional day adds one lodging night and one full M&IE day. This pattern explains why extending a trip can increase both parts of the estimate at once.

Worked example: three TDY days in San Diego

Assume a three-day San Diego trip using the sample lodging rate of $182 and M&IE rate of $79. Three travel days imply two lodging nights, so estimated lodging is 2 × $182, or $364.00. The first and last days each receive 75% of $79, while the middle day receives the full $79. M&IE is therefore $59.25 + $79.00 + $59.25, or $197.50. The combined estimate is $561.50.

The lodging figure should not be read as automatic cash entitlement. If the traveler’s reimbursable room costs $160 per night, actual lodging reimbursement may be $160 rather than the $182 ceiling. Conversely, a room above the ceiling may leave an unreimbursed balance unless an exception or actual-expense authorization applies.

Interpreting the TDY estimate and its assumptions

The result table labels the lodging line as an authorized reimbursement estimate because this page multiplies the entered rate by assumed nights. The M&IE line is the flat-rate portion after applying the two reduced travel days. The total combines those figures but does not include airfare, mileage, rental vehicles, parking, baggage charges, taxes handled separately by policy, or other reimbursable travel costs.

The model also assumes that the same locality applies throughout the trip and that no meal deductions are required. A conference lunch, government dining facility, host-provided dinner, or reduced training rate may lower actual M&IE. A trip involving several cities may need to be separated into daily segments because the applicable lodging ceiling can depend on where the traveler sleeps.

Before travel, compare the estimate with the orders, current locality table, expected hotel receipt, furnished meals, and any reduced-rate instruction. After travel, use the organization’s official voucher process rather than treating this page as a reimbursement determination. The calculator is deliberately narrow: it teaches and estimates the core lodging-plus-M&IE structure without claiming to reproduce every Joint Travel Regulations or agency-policy exception.

Frequently asked TDY per diem questions

Sources: The general structure of a lodging ceiling plus M&IE, including reduced M&IE on the first and last travel day, is described by the U.S. General Services Administration’s Per Diem Rates guidance and the Department of Defense Joint Travel Regulations. Always follow the authority that governs the specific trip.