vehicle_expense_tracking v1.0.0

name: "vehicle_expense_tracking" description: "Track vehicle expenses for business use and choose between the standard mileage rate and actual expenses with the lock-in rules in view: keep a mileage log that satisfies IRS Publication 463, separate business, commuting, and personal miles, run a both-methods comparison with a calculator, track the basis reduction hidden inside the standard rate, and close the year with a clean summary. Use when someone drives a personal or business vehicle for work and needs mileage tracking, a method choice, a year-end vehicle deduction summary, or reimbursement records for an accountable plan. US federal rules; this is recordkeeping and preparation, not tax advice."

Vehicle Expense Tracking

Purpose

Run one vehicle's business use for a full year so the deduction survives scrutiny: a contemporaneous mileage log, costs sorted by method, a both-methods comparison that weighs the first-year lock-in alongside this year's arithmetic, and a year-end summary where every figure traces to the log, the odometer, or a receipt. Rules are IRS Publication 463 and Topic No. 510. Rates and limits change, so the workflow starts by pulling the current figures from the IRS, every time.

Workflow

1. Set up the vehicle file. One file per vehicle: year, make, model, owned or leased, the date it was first available for business use, original cost, and the method used in that first year. That first-year method controls everything later (see references/method-rules.md). Start the basis tracker in references/rates-and-basis.md on day one, even for a standard mileage car.
2. Pull the current rate before touching numbers. Open the IRS standard mileage rates page (https://www.irs.gov/tax-professionals/standard-mileage-rates) and record the business rate for the period the miles were driven. Rates have changed mid-year (2022 and 2026 both split), so check for a split and take a mid-year odometer reading when one applies. Verified reference points: $0.70 for 2025, $0.725 for the first half of 2026, $0.76 for the second half. Never file on a remembered rate.
3. Log every business trip at or near the time it happens. Each entry needs the date, the business destination, the business purpose in specific terms, and the miles, per Publication 463 Table 5-1. A log written up weekly still counts as timely. A log rebuilt from memory in December does not carry the same weight. Use assets/mileage-log.csv as the blank log and assets/example-log.csv as the filled pattern. Record the odometer on January 1 and December 31. Commuting and personal miles do not need trip rows, because total miles come from the odometer, but flag commuting rows when they are logged.
4. Sort trips into three buckets, not two. Business: travel between work locations, to clients, job sites, suppliers, and temporary work locations under the Publication 463 rules. Commuting: home to a main or regular workplace and back, personal by rule, no matter the distance and even if work happens in the car. Personal: everything else. One exception worth checking: if a home office qualifies as the principal place of business, trips from home to another work location in the same business are business trips, not commuting.
5. Collect costs by bucket all year. Operating costs (gas, oil, repairs, tires, insurance, registration, licenses, garage rent) go in one total. Keep business parking fees and tolls out of that total: they are deductible in full under either method and get added after the proration. Keep depreciation or lease payments as their own line, and car loan interest as a separate line, because interest is reported apart from the method comparison for the self-employed.
6. Check the log before year-end math. Run bin/log_check.py <log.csv> --total-miles <odometer total> --year <year>. It flags business rows missing a date, destination, purpose, or miles, cross-checks odometer spans, and computes the business-use percentage. Fix problems in the underlying record. Never edit figures to make the checker pass.
7. Run the comparison both ways. Fill assets/method-comparison-worksheet.md and run bin/compare_methods.py. The depreciation input must be the allowable amount for the year, after the section 280F passenger car limits, not a purchase price divided by a guess. Then read the lock-in section of the worksheet before choosing: a first-year actual expense choice with MACRS, section 179, or the special allowance closes the standard mileage rate for that vehicle permanently, while a first-year standard mileage choice keeps both methods open in later years.
8. Close the year. Complete assets/year-end-summary.md: miles by bucket, the computation for the method used, parking and tolls, the business share of loan interest where it applies, and the basis movement. Update the basis tracker (business miles times the per-mile depreciation rate for standard mileage years). File the log, the receipt totals, both odometer readings, and the summary together.

Worked examples (all outputs produced by the shipped scripts)

Standard mileage wins, ordinary car, 2025. 12,000 business miles out of 16,000 total (75 percent business use), rate $0.70, operating costs $5,700, depreciation $3,000, business parking and tolls $180. bin/compare_methods.py --business-miles 12000 --total-miles 16000 --rate 0.70 --operating-costs 5700 --depreciation 3000 --parking-tolls 180 Standard: $8,400 plus $180 = $8,580. Actual: ($5,700 + $3,000) x 75% = $6,525, plus $180 = $6,705. Standard mileage is larger by $1,875. Adding --loan-interest 900 reports the business share of interest, $675, as a separate line that does not change the winner.

Actual expenses win, costly vehicle, low miles, 2025. 6,000 business miles out of 10,000 total (60 percent), operating costs $7,800, allowable depreciation $9,000, parking and tolls $100. bin/compare_methods.py --business-miles 6000 --total-miles 10000 --rate 0.70 --operating-costs 7800 --depreciation 9000 --parking-tolls 100 Standard: $4,200 plus $100 = $4,300. Actual: $16,800 x 60% = $10,080, plus $100 = $10,180. Actual expenses are larger by $5,880. The trap is timing: if this is the vehicle's first business year, taking this result with accelerated depreciation closes standard mileage for good, and a later high-mileage year cannot reopen it.

Split-rate year, 2026. 5,000 business miles in the first half at $0.725 and 5,000 in the second half at $0.76. bin/compare_methods.py --miles 5000 5000 --rates 0.725 0.76 --total-miles 14000 --operating-costs 6100 --depreciation 2800 Standard mileage: $3,625 + $3,800 = $7,425. One rate applied to the whole year would misstate this by hundreds of dollars in either direction.

Log check. bin/log_check.py assets/example-log.csv --total-miles 500 --year 2025 passes: 5 business rows totaling 231.0 business miles, one commuting row of 18 miles excluded from the business total, business-use percentage 46.20 percent against the odometer total. A business row with an empty destination or purpose fails the check by name and line number.

Basis, from Publication 463 itself. A $30,500 car on standard mileage from 2020 through 2025, driving 14,100, 16,300, 15,600, 16,700, 15,100, and 14,900 business miles, reduces basis by $26,224 at the per-mile depreciation rates for those years ($0.27, $0.26, $0.26, $0.28, $0.30, $0.33). Adjusted basis at the end of 2025: $4,276. The full table and tracker live in references/rates-and-basis.md.

Output Contract

• mileage-log.csv: one row per business trip with date, destination, specific purpose, trip type, and miles, plus January 1 and December 31 odometer readings recorded with the vehicle file.
• method-comparison-worksheet.md (from assets/): miles, cost totals, the calculator output for both methods, the lock-in questions answered in writing, and the method chosen with its reason.
• year-end-summary.md (from assets/): the filed computation for the method used, business-use percentage, parking and tolls, separate interest line where it applies, and the basis at the start and end of the year.
• Basis tracker, updated yearly per vehicle, in the format given in references/rates-and-basis.md.
• Every figure in the outputs traces to the log, an odometer reading, or a receipt total. Estimates are labeled as estimates with their basis, or left out.

Operating Rules

1. Verify every rate and limit against the current IRS source in the run where it is used. Publication 463, the standard mileage rates page, and Topic No. 510 are the sources. A rate from a prior year, a blog, or memory is not a source.
2. The log comes first. No log, no business miles, no comparison. Publication 463 is explicit that amounts you approximate or estimate cannot be deducted, and the records are what prove the business-use percentage under either method.
3. Never count commuting as business use. Home to a regular workplace is personal even when calls are taken in the car or tools are hauled. Check the principal-place-of-business home office exception before reclassifying a home-based trip, and write down why it applies.
4. Never deduct the same cost twice. In a standard mileage year, gas, repairs, insurance, registration, depreciation, and lease payments are already inside the rate. Parking and tolls are the add-on, and only the business ones.
5. Respect the bars. Standard mileage is closed when five or more cars run at the same time, or after MACRS, section 179, or the special allowance touches the vehicle, or after actual expenses were claimed for a leased car. A leased car on standard mileage stays on it for the whole lease including renewals. Check the full list in references/method-rules.md before recommending a method.
6. Watch the 50 percent line on depreciation. At 50 percent or less qualified business use, MACRS, section 179, and the special allowance are off the table, straight line applies, and a drop across the line in a later year can recapture earlier excess depreciation. Flag the risk in the worksheet whenever future personal use is plausible.
7. Basis moves every year, whichever method is used. Record the reduction for standard mileage years at that year's per-mile depreciation rate from references/rates-and-basis.md. For years after 2025, read the component from that year's IRS notice instead of inferring it from the rate.
8. Employees are a different case. Most employees cannot deduct unreimbursed car expenses. Route an employee's personal car costs through an accountable plan reimbursement (business connection, accounting within a reasonable time, excess returned) and keep the same log as the substantiation. The exceptions Topic No. 510 names are reservists, qualified performing artists, fee-basis government officials, and the self-employed.
9. Sampling is a real but narrow tool. Publication 463 allows adequate records for part of a year to prove the whole year only when other evidence shows the sampled periods are representative. If sampling is used, name the sampled periods and the supporting evidence in the summary. It is not permission to log one week and assert a year.
10. Keep the records with the return. Publication 463 puts the general period at 3 years from filing the return that claims the deduction, and business-use records for each year of the recovery period. State rules differ and were not verified here, so check the state's own guidance before stating a state treatment or a state mileage figure.
11. This skill prepares records and comparisons. Filing positions, depreciation elections, and entity questions go to a tax professional with the summary in hand. Say so in the output when the facts get past recordkeeping: related-party use, fleet operations, S corp vehicles, and vehicles over the passenger car limits all qualify.
12. Plain writing only. No em dashes, no marketing phrasing, no filler.