Mobile Welding Bookkeeping: Trigger Time, Consumables as Job Costs, and How to Price an Arc Hour

You quote $90 an hour, you weld for six hours, and the check is $540. After gas, wire, grinding discs, drive time, and the truck payment, you kept maybe half of it — and you won't know exactly how much until tax season forces you to look. That gap between your shop rate and your real earnings is where mobile welding businesses quietly bleed, and it almost always traces back to the books: consumables buried in a generic "supplies" line, unbilled hours nobody tracked, and equipment costs that never made it into a single job's price.

A mobile rig turns every cost most shops treat as overhead into a per-job variable. The gas flows only when you're on site. The truck earns nothing parked in your driveway. The fix isn't working more hours — it's accounting for the ones you already work like a fabricator instead of a hobbyist. Here's how.

Gas, Wire, and Rod Are Direct Job Costs — Book Them That Way​

The single most profitable bookkeeping change a mobile welder can make is also the simplest: stop lumping shielding gas, MIG wire, stick electrodes, TIG filler rod, and tungsten into "shop supplies" alongside office paper and hand soap. Those consumables are consumed by specific jobs, which makes them direct costs of the work — the welding-trade equivalent of cost of goods sold.

Why the category matters in practice:

• Per-job margins become visible. When a gate repair shows $180 of gas and wire against a $540 invoice, you learn something a lumped supplies account can never tell you: which kinds of jobs actually pay. Structural stick work with cheap electrodes and fast travel speed margins very differently from ornamental TIG work that sips expensive filler at low amperage.
• Estimates get honest. A consumables history per process (MIG vs. TIG vs. stick vs. flux-core) lets you build material allowances into quotes from evidence instead of gut feel. Welders who track this typically discover one process subsidizing the others.
• Tax time gets cleaner. Materials that go into a customer's job are deductible as part of the cost of doing that job. Safety glasses, grinding discs used for shop maintenance, and general abrasives that can't be tied to a job still belong in supplies — but everything the arc consumes on a paying job deserves its own line.

Set up three consumable accounts at minimum — shielding gas, wire and electrodes, and abrasives and cutting consumables — and code every gas-supplier and welding-supply receipt to the job it served. If one cylinder spans three jobs, split it by arc hours or by your best reasonable estimate. Approximate allocation beats no allocation every time.

The small-business inventory shortcut​

Strictly speaking, materials you buy, hold, and later consume on jobs are inventory, and inventory normally has to be counted at year-end with only the consumed portion deducted. But most mobile welding operations qualify for the small-business exception: if your average annual gross receipts are under the inflation-adjusted threshold (roughly $30 million — a ceiling virtually every independent rig sits far below) and you aren't a tax shelter, you can treat metals and consumables as non-incidental materials and deduct them when used or consumed on the job.

The practical consequence: you don't need a formal year-end inventory count to stay compliant, but you do need purchase records and a plausible record of what went into jobs. Save every steel-yard and gas-supplier invoice, note the job on the receipt, and keep a simple running log of plate, tube, gas, and wire bought versus billed. That paper trail is what turns a drawer of receipts into defensible deductions.

Price Trigger Time, Not Clock Time​

Ask mobile welders what they charge and you'll hear hourly rates clustering around $60 to $130 an hour, with most 2026 pricing guides landing between $50 and $150 depending on process, certification, and region. Ask what an hour costs them and you'll get silence — which is exactly the problem.

Your hood is down for only a fraction of the hours a job consumes. Around every arc hour sits setup, tacking and fit-up, grinding and cleanup, drive time, loading and unloading the rig, and quoting. Industry veterans call the arc-on portion "trigger time," and it is the only time your consumables math means anything. Pricing trigger time correctly requires knowing your true cost per arc hour first.

Build your cost per arc hour​

Work it bottom-up with your own numbers. An illustrative example for a MIG rig:

• Shielding gas: A 125-cubic-foot cylinder flowing at roughly 20 cubic feet per hour delivers about six arc hours. If the fill costs $60, that's ~$10 per arc hour.
• Wire: A 10-pound spool at typical deposition rates stretches across many arc hours, but contact tips, nozzles, and drive-roll wear add a steady drip — budget a few dollars per arc hour all-in for a small MIG setup, more for dual-shield or hardfacing wire.
• Abrasives and cutting: Grinding discs, cut-off wheels, and saw blades rarely get metered, yet a heavy prep job can eat $15–$25 in abrasives alone. Log them per job for a month and you'll have a reliable average.
• Fuel and rig wear: The engine-driven welder burns fuel whether you're arcing or grinding. Allocate generator fuel and maintenance across arc hours too.

Add it up and a "$90 an hour" welder may be spending $20–$35 of every arc hour on consumables alone — before the truck moves an inch. That number belongs inside your rate, not absorbed by it.

Then wrap the non-arc hours around it​

Three structures cover nearly all mobile work:

1. Hourly with a service minimum. Bill portal-to-portal (or tack on a trip charge of $50–$150) and enforce a one- or two-hour minimum. The minimum exists because mobilizing the rig costs the same whether the repair takes twenty minutes or three hours — many experienced mobile welders won't roll the truck for less than the equivalent of two to three hours. Your books should show the trip charge as its own income line so you can verify it actually covers fuel, mileage, and lost shop time.
2. Per-inch or per-foot pricing for production-style work like pipe or long structural runs, where experienced hands quote $2–$7 per inch depending on process and position. This only works if your cost-per-arc-hour math already includes consumables — otherwise a fast travel speed just means you lose money faster.
3. Flat project quotes built from estimated arc hours × loaded rate, plus materials with markup, plus mobilization. Never quote flat work without the arc-hour cost exercise above; flat quotes are where untracked consumables do the most damage.

Review the split quarterly. If non-arc time keeps growing as a share of the week — longer drives, chattier job sites, more estimate trips — the hourly rate has to rise even if consumables stay flat.

The Truck Is a Profit Center or a Money Pit — Your Mileage Log Decides​

For a mobile welder, the truck and trailer are the shop: rent, utilities, and storefront rolled into one depreciating asset. The IRS lets you deduct business driving two ways — the standard mileage rate or actual expenses (fuel, insurance, repairs, depreciation) — and mobile rigs with heavy welder/generator setups often find actual expenses win, since fuel and maintenance run far above average. But you can't choose wisely without records, and the choice has to be consistent year to year once depreciation enters the picture.

What to track regardless of method:

• Every business mile, contemporaneously — date, destination, purpose, odometer. An app log beats a reconstruct-January shoebox every time, and commuting from home to a regular shop location generally doesn't count.
• The rig itself separately from the tow vehicle. An engine-driven welder, air compressor, and trailer-mounted setup are equipment, not vehicle expense. A $15,000–$30,000 rig purchase may qualify for first-year Section 179 expensing rather than multi-year depreciation — a decision that can swing a year's taxable income by five figures, so model it with your tax preparer before December, not after.
• Cylinder leases and demurrage. Monthly cylinder rent is an ordinary business expense, but many welders pay it for years without noticing it rivals the cost of buying. Audit the lease-versus-own math annually.

Repairs deserve their own discipline too. A $400 stator rewind that keeps the machine earning is a current repair; a $4,000 engine replacement that extends the rig's life may need capitalizing. When in doubt, ask before filing — the classification changes the deduction's timing, and timing is money.

The Deductions Welders Leave on the Table​

Beyond consumables and the truck, independent welders routinely under-claim in the same handful of places:

• Certifications and training. AWS certification fees, CWI exam prep, procedure-qualification testing, and refresher courses that maintain your current trade are deductible education. Training for a wholly different occupation generally isn't — the line is whether it maintains or improves skills in your present work.
• Protective gear and uniforms with limits. FR jackets, welding hoods, respirators, and dedicated leathers required for the work qualify. Everyday clothing that happens to get sparks on it doesn't, even if you only wear it welding — courts have repeatedly denied deductions for steel-toed boots and FR clothing that are adaptable to general wear, so keep the claim to gear that's genuinely unsuitable off the jobsite.
• Insurance. General liability, inland-marine coverage on the rig, and commercial auto premiums are all ordinary business expenses. If a single incident could total the rig and your liability in one afternoon, the premium is cheap — and fully deductible.
• Home office and communication. If you quote, invoice, and run the business from a dedicated home space used regularly and exclusively for the work, the simplified or actual home-office deduction applies. The phone that takes customer calls and photos of every job is partly a business asset — document the business-use percentage.
• The self-employment tax surprise. Net earnings above $400 trigger self-employment tax — 15.3% for Social Security and Medicare on top of income tax. First-year independents who price jobs like W-2 welders (gross pay equals take-home) get blindsided every April. Build estimated quarterly payments into your cash flow from the first profitable month, and remember the employer-equivalent half of self-employment tax is itself deductible.

Keep receipts for all of it. The welder-specific guidance from trade suppliers has said the same thing for over a decade because it stays true: no receipt, no deduction — and a photo of the receipt stored with the job record counts.

Build a Books Routine That Survives Busy Season​

None of this requires accounting software wizardry. It requires a weekly habit that survives the months when you're welding six days straight:

1. Separate money on day one. A dedicated business checking account (and card) turns "find the business expenses" from an archaeology project into a bank export. Commingling is the root cause of most missed deductions.
2. Invoice from the truck. Same-day invoices with separate lines for labor, materials, consumables allowance, and trip charge get paid faster and create the job-cost record automatically. Reconcile deposits to invoices monthly — payment-app and card income arrives with fees skimmed and 1099-Ks that report the gross, so your books must show both.
3. Close the month in 30 minutes. Reconcile the bank account, code the consumable receipts to jobs, log mileage, and glance at two numbers: effective rate per total hour worked (revenue divided by all hours including driving and quoting) and consumables as a percentage of revenue. If the effective rate drifts toward your old W-2 wage, your pricing — not your welding — needs work.
4. Estimate taxes quarterly, review annually. Quarterly payments avoid penalties; an annual sit-down with a tax professional before year-end is where Section 179 timing, retirement contributions, and entity-structure questions (sole proprietorship vs. S corporation once profits support it) actually get decided.

Simplify Your Financial Management​

Once gas, wire, mileage, and rig costs each have their own line in your books, pricing stops being guesswork — every quote can carry its true cost and every quarter tells you which work to chase. Beancount.io gives you plain-text, version-controlled accounting with zero black boxes, so your job-cost history stays transparent and fully under your control. Get started for free and run your rig on numbers as solid as your welds.