## TL;DR

IRS rules require the amount, time and place, and business purpose of each trip; the log is missing one or more. Fill in the date, origin, destination, business purpose, and miles (with odometer readings where available) for every trip, then resubmit the log.

## Error

```text
mileage log failed irs substantiation check
```

## Steps

1. Review the IRS substantiation requirements: date, destination, business purpose, and miles for each trip. Expected: you know the four required elements.
2. Audit your log for gaps: trips missing a purpose, vague destinations, or no mileage figure. Expected: the incomplete trips are identified.
3. Fill the gaps from calendars, maps, and odometer records while the trips are still reconstructable. Expected: every trip has all four elements.
4. Record odometer readings at the start and end of the period if your log supports them. Expected: the totals tie to the odometer.
5. Resubmit the log. Expected: it passes the substantiation check.

## When to use

- A mileage log fails an IRS substantiation or audit review.
- Trips are missing purpose, destination, or mileage details.

## When not to use

- The mileage rate is wrong (see the rate-mismatch skill).
- The log is complete but the approver questions specific trips (address those trips).

## Tool compatibility

- Expensify, Concur mileage modules; IRS Publication 463 rules.

## Variant phrasings

### Mileage log lacks adequate records

The reviewer phrasing of the same failure.

### Substantiation failed on mileage

Shorter wording for the same check.

## Why it happens

The IRS disallows mileage deductions without adequate records, and reviewers apply the same standard to reimbursements. Estimates and purpose-free logs fail because they cannot prove the business connection.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_vBG4OQSQNHgTlraVJqx3Fg