Per Diem Calculator

The Per Diem Calculator works out the total daily allowance for a business trip from three simple inputs — your lodging rate, your meals & incidental expenses (M&IE) rate, and the number of days you travel. What sets it apart from a quick "days × rate" multiplication is that it follows the real U.S. GSA federal rule: lodging is paid for each overnight stay and is never reduced, while the first and last travel days are paid at only 75% of the M&IE rate. You get a per-day trip timeline, a lodging-versus-M&IE breakdown, and a full step-by-step calculation in your chosen currency.

What Is Per Diem?

Per diem (Latin for "per day") is a fixed daily amount an employer pays a traveling employee to cover lodging, meals, and small incidental expenses, instead of reimbursing every individual receipt. Governments and most companies set standard per-diem rates by destination so that travel costs are predictable and paperwork is light. The allowance is split into two parts: a lodging component and a meals & incidental expenses (M&IE) component.

How the First & Last Day Proration Works

On the day you depart and the day you return, you are only traveling for part of the day, so you do not need a full day of meals. The U.S. General Services Administration (GSA) therefore pays only 75% of the daily M&IE rate on the first and last calendar day of a trip. Lodging is different — every night you actually stay away is paid in full, with no proration. This calculator applies both rules automatically, and lets you switch the 75% figure to "no proration" or any custom percentage your organization uses.

Per Diem Formula

The total per diem is the lodging total plus the M&IE total. Lodging counts overnight stays; M&IE prorates the two travel days.

For a single-day trip there is no overnight stay, so lodging is zero and the one travel day is paid at 75% of the M&IE rate.

Worked Example

A 5-day conference with a $150 lodging rate and a $79 M&IE rate (GSA 75% proration):

How to Use This Calculator

1. Enter the trip length: The total number of days from departure to return.
2. Enter your daily rates: The lodging rate per night and the M&IE rate per day for your destination (look these up on your agency's or company's per-diem schedule).
3. Choose proration: Keep the GSA standard 75% for travel days, pick "no proration," or enter a custom percentage.
4. Click Calculate: Review the total per diem, the day-by-day timeline, the lodging-versus-M&IE split, and the step-by-step math.

Frequently Asked Questions

What is per diem?

Per diem is a fixed daily allowance an employer pays to cover an employee's lodging, meals, and incidental expenses while traveling for work, instead of reimbursing each receipt individually. It is split into a lodging rate and a meals and incidental expenses (M&IE) rate.

How is per diem calculated for the first and last day?

Under the U.S. GSA federal rule, the first and last day of travel are paid at only 75% of the daily M&IE rate, because you are not away for the full day. Lodging, however, is paid in full for each overnight stay and is never prorated.

How many nights of lodging does a trip include?

A trip of N days normally includes N − 1 nights of lodging, because you check out and travel home on the final day. For example, a 5-day trip has 4 overnight stays.

What does M&IE stand for?

M&IE stands for Meals and Incidental Expenses. It covers the cost of meals plus small incidental costs such as tips and fees. It is one of the two components of per diem, the other being lodging.

Is per diem taxable?

Per diem paid at or below the federal rate and supported by an expense report is generally not taxable to the employee. Amounts paid above the federal rate, or paid without the required documentation, may be treated as taxable wages. Always confirm with your employer or a tax professional.

Can I change the 75% proration rate?

Yes. The calculator defaults to the GSA standard of 75% for travel days, but you can switch to no proration so every day pays the full M&IE rate, or enter any custom percentage your organization uses.

Additional Resources

• Per Diem - Wikipedia
• GSA Per Diem Rates