The rule of thumb is not wrong so much as it is unaimed. It ignores the single largest deduction most over-the-road drivers have, it applies one flat percentage to a tax that is part flat and part progressive, and it takes no account of the safe harbour — the rule that caps what a taxpayer is required to pay in during the year, whatever the final bill turns out to be.
This page sets out the six-step calculation with the actual 2026 figures, works it through on a representative owner-operator, and gives you the workpaper we use to run it. Every rate and threshold below is cited to its primary source.
Representative owner-operator: $265,000 gross revenue, 110,000 business miles, $184,480 of operating cost including depreciation, 260 nights out, married filing jointly, no prior-year return on file. Full waterfall below.
The six steps
Order matters here. Per diem comes first because it changes net profit, net profit drives self-employment tax, and self-employment tax feeds back into adjusted gross income. Run these out of sequence and the answer is wrong.
Per diem, before anything else
A driver subject to Department of Transportation hours-of-service limits may claim the special transportation-industry meal allowance rather than tracking receipts. For travel on or after 1 October 2025 the rate is $80 per full day within the continental United States and $86 outside it.
Two details are routinely missed. Departure and return days must be prorated: the Federal Travel Regulations method allocates 75% of the full-day rate, and the revenue procedure also permits any other method applied consistently. And the deductible share is 80%, not the general 50% — the hours-of-service exception substitutes 80 percent for 50 percent.
One limit worth stating to the client plainly: this deduction lives on Schedule C. A company driver receiving a W-2 cannot take it, because unreimbursed employee expenses remain non-deductible. It is available to owner-operators and to carriers reimbursing under an accountable plan.
Sources: IRS Notice 2025-54; Rev. Proc. 2019-48 §6.04; IRC §274(n)(3); IRC §67(g).
260 full days at $80 plus 40 partial days at $60 gives a gross allowance of $23,200. At 80%, the deduction is $18,560. Treated at 50% instead, the driver loses $5,800 of deduction and roughly $1,000 of tax.
Net profit on Schedule C
Gross settlements, including fuel surcharge, less every operating cost and less the per diem from step 1. Depreciation and any Section 179 or bonus election come across from the depreciation schedule — that is a separate calculation and should not be estimated here.
This is also the point to produce a cost-per-mile figure. It costs nothing extra once the expense schedule is built, and it is the number an owner-operator will actually act on.
Self-employment tax
Net earnings from self-employment are 92.35% of net profit. On that:
- 12.4% Social Security, up to the 2026 wage base of $184,500, reduced by any W-2 wages already subject to Social Security
- 2.9% Medicare, with no ceiling
- 0.9%additional Medicare above $200,000 — $250,000 for a joint return, $125,000 filing separately. These thresholds are statutory and are not indexed for inflation, so they capture more drivers every year
Half of the Social Security and Medicare components is deductible in step 4. The additional Medicare tax is not.
Sources: IRC §§1401, 1402(a)(12), 164(f); SSA contribution and benefit base, 2026.
Taxable income
Net profit, less the deductible half of self-employment tax, plus other household income, gives adjusted gross income. Then the 2026 standard deduction — $32,200 joint, $16,100 single or filing separately, $24,150head of household — unless itemising is better.
Then the qualified business income deduction: 20% of qualified business income, capped at 20% of taxable income. For most owner-operators this is a clean 20%. Above the 2026 threshold amounts of $201,750 (or $403,500 joint) the wage and property limitations phase in and the simple calculation stops being reliable.
Sources: Rev. Proc. 2025-32 §§2.01, 2.11, 2.15.
Federal income tax on the 2026 brackets
Apply the 2026 rate schedule to taxable income. This is where the rule of thumb goes furthest wrong: after the standard deduction and the QBI deduction, a great many owner-operators land entirely in the 10% and 12% bands. Self-employment tax is the larger half of their bill by a wide margin.
The safe harbour — what must actually be paid in
The required annual payment is the lesser of two tests:
- 90% of the tax shown on the current-year return, or
- 100% of the prior year’s total tax — rising to 110% where prior-year AGI exceeded $150,000, or $75,000 filing separately
The prior-year test is only available where the preceding year covered a full twelve months and a return was actually filed. For a driver in their first year under their own authority, the 90% current-year test is the only one on the table.
Subtract any federal withholding, then divide by four. No estimated payments are required at all where the 2026 tax shown on the return, less withholding, comes to less than $1,000 — note that the test is measured before estimated payments, not after.
Sources: IRC §§6654(d)(1)(B), 6654(d)(1)(C)(i), 6654(e)(1), 6654(h).
A driver coming off a strong year into a weak one pays on the 90% current-year test. A driver coming off a weak year into a strong one pays on the prior-year figure and keeps the difference in the business until filing. The rule of thumb captures neither.
The calculation, worked
| Line | Amount |
|---|---|
| Gross settlements, including fuel surcharge | $265,000 |
| Operating costs, including $21,000 depreciation | ($184,480) |
| Per diem — 260 full days, 40 partial, at 80% | ($18,560) |
| Net profit — Schedule C | $61,960 |
| Net earnings from self-employment (92.35%) | $57,220 |
| Social Security, 12.4% | $7,095 |
| Medicare, 2.9% | $1,659 |
| Self-employment tax | $8,755 |
| Net profit, less deductible half of SE tax | $57,583 |
| Standard deduction, joint | ($32,200) |
| QBI deduction — 20%, capped at 20% of taxable income | ($5,077) |
| Taxable income | $20,306 |
| Federal income tax — 10% band | $2,031 |
| Projected total 2026 tax | $10,785 |
| Required annual payment — 90% current-year test | $9,707 |
| Quarterly instalment | $2,427 |
Federal income tax and self-employment tax only. State income tax, IFTA fuel tax and Heavy Highway Use Tax are separate. Figures rounded to the dollar.
Two things stand out. Self-employment tax is 81%of this driver’s federal bill — income tax is almost an afterthought. And the total, $10,785, is 17.4% of net profit, not 25%. Reserving on the rule of thumb would have parked $5,783 with the IRS that the business could have used for a tyre account or a maintenance reserve.
The gap runs the other way for a driver with a working spouse, significant other household income, or profit high enough to reach the 22% and 24% bands. The same 25% that over-reserves the driver above leaves that driver short. A percentage that is wrong in both directions is not a percentage worth using — which is the argument for running the calculation once a year and giving the client a number that fits them.
The 2026 payment calendar
| Instalment | Income period | Due |
|---|---|---|
| Q1 | 1 January – 31 March 2026 | Wed 15 Apr 2026 |
| Q2 | 1 April – 31 May 2026 | Mon 15 Jun 2026 |
| Q3 | 1 June – 31 August 2026 | Tue 15 Sep 2026 |
| Q4 | 1 September – 31 December 2026 | Fri 15 Jan 2027 |
Q2 covers two months, not three — it is the instalment most often missed. The Q4 instalment alone is not required if the 2026 return is filed and paid in full by 1 February 2027 — IRC §6654(h); 31 January falls on a Sunday. It does not relieve a penalty on the first three. Pay at irs.gov/payments and keep the confirmation number — it is the only proof of the payment date.
Four other deadlines belong on the same page for a trucking client, because missing them costs more than a late instalment: IFTA returns on 30 April, 31 July, 2 November 2026 and 1 February 2027 (the last two shift off a weekend), and Form 2290 by 31 August 2026 for a vehicle first used in July.
Four things that go wrong
Meals taken at 50%
Generic tax software and generic bookkeepers apply the standard 50% limit. Drivers subject to DOT hours-of-service rules get 80%. On 260 nights out that difference is worth about $1,000 in tax every year, and it compounds quietly across every year nobody checks.
Reserving against gross, not net
Owner-operator gross revenue runs three to four times net profit. A percentage set against settlements rather than profit is arbitrary. In the example above the correct reserve is 3.7% of gross — but that number is only meaningful because it was derived from the profit calculation, not guessed at.
Missing the 110% step-up
A good year pushes prior-year AGI above $150,000, and the prior-year safe harbour quietly moves from 100% to 110%. A preparer who rolls forward last year’s instalments without re-testing hands the client an underpayment penalty on a year they did nothing wrong.
Treating an uneven year as an even one
Freight is seasonal and equal instalments assume income is not. Where a driver earns disproportionately in the second half, the annualised income instalment method on Form 2210 Schedule AI usually produces smaller early payments and no penalty. It takes longer, and it is frequently worth it.
The workpaper
The spreadsheet we use to run this. Enter a projected year of settlements, miles, operating costs and nights out; it returns the instalment, the cost-per-mile schedule and the client-facing payment calendar.
- Every 2026 rate, bracket and threshold on one tab, each with its citation — update that tab and the workbook follows
- Per diem at the DOT 80% rate with partial-day proration
- Self-employment tax including the wage-base cap and the additional Medicare tax
- Both safe-harbour tests, with the 110% step-up applied automatically
- A rule-of-thumb comparison, so you can show the client the gap rather than assert it
Free, no email required. Built for Schedule C sole proprietors and single-member LLCs; an S-corp election changes the self-employment calculation and this workbook should not be used for one.
Sources
- IRS Notice 2025-54 — special per diem rates, 1 October 2025 to 30 September 2026
- Rev. Proc. 2019-48 §6.04 — proration of partial travel days
- Rev. Proc. 2025-32 — 2026 inflation adjustments: rate schedules, standard deduction, §199A thresholds
- IRC §274(n)(3) — 80% meal deduction for individuals subject to DOT hours-of-service limits
- IRC §67(g) — suspension of miscellaneous itemised deductions, made permanent in 2025
- IRC §§1401, 1402(a)(12), 164(f) — self-employment tax and the deductible half
- IRC §§6654(d), 6654(e)(1), 6654(h) — required annual payment, de minimis, and the January filing exception
- Social Security Administration — contribution and benefit base, 2026: $184,500