Section 179 or Bonus Depreciation: Choosing How to Write Off Your Next Dump Truck

Every fall, the same conversation happens in pickup trucks and job trailers across the country: a contractor looks at how the year is shaping up, looks at the truck that's been limping along since spring, and starts asking whether now is the time to buy. The equipment decision is usually the easy part. The harder question — the one that actually determines how much that new truck costs you after taxes — is whether you write it off using Section 179, bonus depreciation, or some combination of the two. Both tools can let you deduct a large share of a truck's cost in the year you put it to work instead of spreading it out over five or six years. But they're not the same tool, they don't always produce the same result, and the choice between them can matter more than people expect. This article walks through how each one works, where they overlap, and what actually drives the decision for a working dump truck purchase — with the understanding that the final call always belongs to your tax professional, not a truck dealer or a lender.

Two Different Tools, Same Basic Goal

Section 179 and bonus depreciation both exist to accelerate a deduction that would otherwise trickle out over the useful life of the asset. Without either one, a dump truck purchase gets depreciated on a schedule — a portion written off each year for several years. Section 179 and bonus depreciation both let you pull a much bigger chunk of that deduction into the year the truck is placed in service. Where they differ is in the mechanics: how the deduction is calculated, what it's limited by, and how it behaves if your business has a rough year.

Section 179 is an election. You choose how much of the truck's cost to expense under Section 179, up to the annual dollar limits set by the IRS for that tax year, and that election is tied to specific properties. Section 179 also has a business income limitation — you generally can't use it to create a net loss for the business, though any amount you can't use typically carries forward. Bonus depreciation works differently: it applies automatically to qualifying property unless you elect out of it, it isn't capped by an annual dollar limit the way Section 179 is, and it can create or increase a net operating loss. Those two differences — the income limitation and the loss treatment — are often what push the decision one way or the other for a given year.

How Section 179 Actually Works for a Truck Purchase

Section 179 was built with equipment-heavy small businesses in mind, and a vocational truck qualifies as long as it's used more than 50% for business. The annual dollar limits and the point at which the deduction starts phasing out change from year to year with inflation adjustments and legislative updates, so we're not going to print a specific number here and risk it being stale by the time you read this — your tax professional will have the current-year figures. What matters conceptually is that Section 179 gives you a dollar-for-dollar election: you decide how much of the truck's cost to expense immediately, subject to those limits, and the rest depreciates normally.

The income limitation is the detail contractors most often overlook. Section 179 can only offset business income down to zero — it can't be used to manufacture a loss. If your business had a lean year and taxable income is already low, a big Section 179 election on a new truck might not do what you're hoping it will do, at least not all in the current year. That's a conversation to have with your tax professional before you assume the full deduction is available.

How Bonus Depreciation Works — and Why the Percentage Matters

Bonus depreciation has gone through several versions over the past decade, with the applicable percentage stepping up, phasing down, and getting adjusted again by subsequent legislation. Unlike Section 179, bonus depreciation isn't an item-by-item election in the same way — it applies to an entire class of qualifying property in a given tax year at whatever the current bonus percentage is, and it isn't limited by business income the way Section 179 is. That's a meaningful difference for a contractor whose income varies year to year: bonus depreciation can still apply even in a year where Section 179's income limitation would cap you out.

Because the bonus percentage itself has changed materially across recent tax years — and because Congress has shown it's willing to revisit it again — this is exactly the kind of detail where a stale blog post or a dealer's rule-of-thumb can steer you wrong. Confirm the current-year bonus depreciation percentage with your tax professional before you build a purchase decision around it.

Where Financing Fits Into the Decision

Here's something contractors sometimes get backwards: taking a large first-year deduction doesn't require paying cash for the truck. You can finance the full purchase price with a conventional equipment loan and still generally take the Section 179 or bonus depreciation deduction on the truck's full cost, not just the amount you put down, as long as you meet the ownership and placed-in-service requirements your tax professional will walk you through. That's part of why financing and tax strategy are usually discussed in the same breath around here — the deduction and the deposit are two separate decisions, and treating them as one can lead to putting more cash into a truck than the deal actually requires.

We've written before about the real tradeoffs between leasing and a straight loan, and the structure you choose there interacts directly with which depreciation approach makes sense — a true lease and a $1 buyout lease can be treated very differently for tax purposes, which is one more reason this isn't a decision to make from a spec sheet alone.

A Realistic Example: Putting a Truck Like the Kenworth T880 Into Service

Say a site-work contractor is replacing an aging dump truck with a new Kenworth T880 — a common choice in this weight class because Kenworth builds the T880 across a wide span of vocational configurations, from a standard set-back front axle model built for tough-duty solutions to the set-forward front axle T880S that's designed around bridge-law-compliant wheelbases for contractors who need to maximize legal payload. Kenworth markets the T880 explicitly for dump truck, mixer, and heavy-haul work, which is exactly the profile of a contractor thinking through this decision.

Kenworth designs the T880 chassis to support this kind of range from the factory specifically because so many T880s leave the assembly line and go straight to an upfitter for a dump body, wrecker bed, flatbed, or mixer drum — which is its own financing wrinkle we'll get into in a future article. For now, the point is simpler: whichever hood configuration, axle setup, and body a contractor specs, the truck itself is squarely the kind of qualifying business property Section 179 and bonus depreciation were both built to cover.

Section 179 vs. Bonus Depreciation: What Actually Drives the Choice

In practice, the decision usually comes down to a short list of questions your tax professional will ask: What does taxable income look like this year, and is it high enough that the Section 179 income limitation won't be a problem? Is there a reason to preserve some depreciation for future years instead of taking it all now — for instance, if you expect a much higher-income year ahead where the deduction would be worth more? And does the current bonus depreciation percentage make it more efficient to lean on bonus depreciation for part of the truck's cost and Section 179 for the rest, since many tax professionals use both tools together rather than picking one exclusively.

None of those questions have a generic answer, which is exactly why this article isn't going to pretend to give you one. What we can tell you with confidence is that the truck itself — a T880, a comparable Mack Granite, or anything else in this class — qualifies as the kind of business-use vocational equipment both provisions were designed for. The tax mechanics are where a professional needs to be in the conversation.

The Financing Conversation Comes First, the Filing Comes Later

From where we sit, the practical order of operations looks like this: figure out which truck actually fits the work — we compared the Kenworth T880 against the Freightliner 114SD Plus in detail if you're cross-shopping — get pre-qualified so you know your real budget and deposit range, and then loop your tax professional in on the depreciation strategy once the deal terms and the placed-in-service date are close to final. That placed-in-service date matters more than people expect, especially when a truck arrives as a chassis and gets a dump body added afterward; the paperwork and titling timeline for a second-stage build can push a truck's in-service date later than you planned, which can bump the deduction into a different tax year entirely.

It's also worth noting this isn't the first time we've covered Section 179 on this blog — we walked through how it applies to Bobcat Certified Pre-Owned equipment in an earlier article, and a lot of the same fundamentals about the income limitation and the ownership requirement carry over directly to a truck purchase.

Confirm the Details With Your Tax Professional

We'll say it plainly because it matters: the specific dollar limits, phase-out thresholds, and bonus depreciation percentages referenced conceptually in this article change from year to year, and getting them wrong can cost you real money or trigger an amended return. Nothing here is tax advice — it's a framework for the conversation you should be having with a CPA or tax professional who knows your business's full financial picture. What we can help with is the equipment side: finding the right truck, structuring financing that doesn't force you to overpay in cash to capture a deduction, and timing the deal so your tax professional has clean numbers to work with.

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