State IFTA audits typically come with about 30 days' notice. When the letter arrives, missing records or calculation errors can cost you thousands in penalties and unfavorable assessments. The carriers who survive audits without major damage are the ones who caught their own problems first.
Many carriers run their own IFTA audit twice a year. Once mid-year to fix problems while there's time, and once before filing to make sure everything's clean. Here's how to audit your IFTA records like a state auditor would, so you can fix issues before they become expensive problems. For complete IFTA guidance, see our comprehensive IFTA guide for small fleets.
Start With Your Mileage Records
State auditors typically start with mileage because it's the foundation of your entire IFTA calculation. Pull every trip record for the quarter and check these critical points:
Trip completeness: Every dispatched load should have a corresponding mileage record. Missing trips are red flags auditors catch immediately. Cross-reference your dispatch records against your mileage logs to spot gaps.
Route accuracy: Compare your recorded miles against standard routing tools. Auditors commonly use PC*MILER or similar routing software to verify your routes. If your miles are consistently higher or lower than standard routing, you need documentation explaining why. Detention, fuel stops, or required routing can justify differences, but you need proof.
Personal vs. business miles: Make sure personal use miles are clearly separated and excluded from IFTA calculations. Auditors will ask about trips that don't match business patterns, like weekend driving to non-commercial destinations.
Apportioned vs. non-apportioned miles: Only miles driven with apportioned plates count toward IFTA. Miles driven with temporary permits or in non-IFTA jurisdictions like the District of Columbia should be excluded from your calculations.
Verify Your Fuel Purchase Records
Fuel records are where most IFTA problems surface. Auditors know carriers often lose receipts or make attribution errors. Check your fuel records systematically:
Receipt completeness: Every fuel purchase needs a receipt showing date, location, gallons, and vehicle identification. Credit card statements aren't enough. Auditors want the actual fuel receipt. Missing receipts get assessed at unfavorable default rates.
Location accuracy: Make sure each fuel purchase is attributed to the correct state or province. A fuel stop near a state border needs to be assigned to where you actually purchased fuel, not where you were headed. GPS coordinates on receipts help verify this.
Duplicate entries: Check for fuel purchases entered multiple times, especially if you use both manual logs and automated systems. Duplicate fuel entries inflate your tax credits and trigger audit flags.
Reasonable fuel usage: Calculate your fleet's average MPG and compare it to your recorded fuel and mileage. Auditors flag operations with unusually high or low MPG because it often indicates missing fuel receipts or mileage errors.
Cross-Check Your Tax Calculations
IFTA tax calculations follow a specific formula: miles driven in each jurisdiction divided by total fleet miles, multiplied by total fuel consumed, times the jurisdiction's tax rate, minus fuel taxes already paid in that jurisdiction. Audit your math step by step:
Jurisdiction mile percentages: Add up all your jurisdiction miles and make sure they equal your total IFTA miles. If they don't match, you have attribution errors somewhere.
Tax rate accuracy: Verify you're using current tax rates for each jurisdiction. Tax rates change quarterly, and using outdated rates creates calculation errors auditors catch immediately.
Fuel tax credits: Make sure fuel taxes paid match the jurisdiction where you bought the fuel. Buying fuel in a high-tax state but crediting it to a low-tax state is a common error that inflates your refund claims.
Net tax calculations: For each jurisdiction, verify that your net tax owed (or refund due) makes sense. Large refund claims or unusually high tax bills compared to your mileage patterns often indicate calculation errors.
Document Everything You Find
The audit isn't complete until you've documented every correction and can explain every unusual pattern. Create a file for each issue you found and how you fixed it:
Correction worksheets: Show your work for any corrections you made. If you found missing fuel receipts and estimated the gallons based on trip length and historical MPG, document your methodology.
Exception explanations: Any unusual patterns need written explanations. If you drove 500 extra miles in Colorado because of a required detour, keep the dispatch notes or delivery instructions that prove it.
Source documentation: Keep copies of everything you used to verify your records: dispatch logs, maintenance records, fuel receipts, route confirmations. Auditors want to see the same sources you used.
Running your own IFTA audit takes time, but it's cheaper than letting the state find your mistakes. Carriers who self-audit regularly tend to face fewer surprises and build credibility with auditors who see they're serious about compliance.
Modern TMS systems like HaulerPro help prevent audit problems by automatically capturing per-jurisdiction miles from dispatched loads and organizing fuel receipts by load. The IFTA tracking features export clean mileage data that makes self-auditing faster and more accurate. Start your 14-day free trial. No credit card required.