Per Diem Calculator: GSA Rates, Meal Deductions, and IRS Mileage

How It Works

1. Select Destination and Dates

   Enter the city or county where you are traveling and the trip start and end dates. The calculator looks up the applicable GSA lodging and M&IE tier for that location.

2. Review GSA Rates or Apply Custom Overrides

   The calculator displays the GSA lodging rate and M&IE rate for your destination. If your employer uses custom rates (above or below GSA), enter the override amounts.

3. Enter Employer-Provided Meals

   If the employer or client provides any meals (conference breakfast, team dinner, etc.), check those days and meal types. The calculator deducts the appropriate meal value from the M&IE rate per GSA deduction schedules.

4. Apply First/Last Day Proration

   The calculator automatically applies the 75% rule for the first and last day of travel. Only 75% of the M&IE rate is allowed on travel days per IRS and GSA guidelines.

5. Add IRS Mileage

   Enter round-trip miles driven to the jobsite. The calculator applies the current IRS standard mileage rate and adds it to the per diem total.

6. Review Trip Total and Export

   See the daily breakdown and trip total including lodging, M&IE (with deductions), and mileage. Export as a PDF for expense reports or payroll processing.

Built For

• Traveling pipefitters and boilermakers calculating their per diem allowance before accepting a turnaround job 300 miles from home
• Construction company payroll departments processing weekly per diem for 50 traveling workers across multiple jobsites
• Project managers estimating total travel costs when bidding a job that requires bringing in specialty crews from out of state
• Accounts payable clerks verifying per diem claims against GSA rates before issuing reimbursement checks
• Self-employed contractors tracking per diem for tax deduction purposes with proper documentation
• Union hall dispatchers explaining per diem entitlements to members heading to out-of-area assignments
• Government contracting officers verifying that subcontractor per diem claims do not exceed GSA maximums

Features & Capabilities

GSA 5-Tier Rate Lookup

Uses the current GSA per diem rate structure with 5 tiers of lodging and M&IE rates based on destination location. Covers standard CONUS rates and higher-cost area rates.

75% First/Last Day Rule

Automatically prorates M&IE to 75% on the first and last day of travel per IRS and GSA guidelines. No more manual calculations for partial travel days.

Meal Deduction Tracking

Deducts specific meal values when meals are provided by the employer or included in conference fees. Uses GSA meal deduction schedules for breakfast, lunch, and dinner.

Custom Rate Overrides

Allows custom lodging and M&IE rates for employers who pay above or below GSA. Flags the taxable excess when custom rates exceed GSA maximums.

IRS Standard Mileage

Adds mileage reimbursement at the current IRS rate to the per diem total. Keeps travel and lodging costs in one report.

Where to Look Educational Panel

Built-in reference panel explaining where to find GSA rates, how to document per diem for taxes, and what makes per diem taxable vs non-taxable.

Assumptions

• GSA per diem rates are used as the baseline — 5-tier structure with lodging and M&IE rates varying by destination county.
• First and last travel day M&IE is prorated to 75% of the full daily rate per IRS and GSA guidelines.
• Meal deductions use GSA deduction schedule values for breakfast, lunch, and dinner when meals are provided by the employer or included in event fees.
• IRS standard mileage rate is applied for personal vehicle travel — does not model actual vehicle expense reimbursement.
• Per diem amounts at or below GSA rates under an accountable plan are assumed non-taxable to the employee.

Limitations

• GSA rate tiers are reference values — actual rates change every October 1 and must be verified at gsa.gov for the current fiscal year.
• Does not automatically look up GSA rates by location — the user must enter or verify the applicable rate tier for their destination.
• Non-CONUS (OCONUS) per diem rates (Hawaii, Alaska, US territories, and foreign travel) use different rate schedules not included in this calculator.
• Does not evaluate whether the employer's plan meets IRS accountable plan requirements (business connection, substantiation, return of excess).
• Custom rate overrides do not automatically flag the taxable excess above GSA — the user must note this for payroll processing.

References

• GSA Per Diem Rates — gsa.gov/perdiem (CONUS lodging and M&IE rate tables, updated annually).
• IRS Publication 1542 — Per Diem Rates (substantiation methods for per diem allowances).
• IRS Revenue Procedure 2024-48 — standard mileage rate for business use of a personal vehicle.
• IRS Publication 463 — Travel, Gift, and Car Expenses (per diem rules, 75% first/last day, accountable plan requirements).
• 41 CFR 301-11 — Federal Travel Regulation: Per Diem Expenses (federal employee per diem rules that many private employers follow).

Frequently Asked Questions