What to set aside, and how much

The money in the account is not your money. Some of it belongs to the IRS, some to a set of tires you haven't bought yet, and some to a week you'll spend in a shop three months from now.

Owner-operators rarely fail because they can't find freight. They fail because a $9,000 repair arrives in a month when the account holds $2,000 and the quarterly tax payment is due Tuesday. This guide is about making sure that doesn't happen.

Four things to set aside

Every dollar of revenue should be mentally split before you spend any of it:

Separate bank accounts help more than willpower does. Money that's visible gets spent.

Taxes: why it's more than you think

Nobody withholds anything from a settlement. You're responsible for the whole bill, and there are two parts to it.

Self-employment tax is 15.3% — 12.4% Social Security plus 2.9% Medicare. As an employee you'd pay half and your employer would pay half. Self-employed, you pay both halves. It applies to 92.35% of your net profit, and the Social Security portion stops after $184,500 of earnings in 2026. Medicare has no cap.

Income tax is on top of that, at whatever bracket your total income lands in.

This is why "set aside 25–30% of net profit" is the standard advice. Self-employment tax alone is over 15% before a dollar of income tax.

One piece of good news: half of your self-employment tax is deductible against income tax, which softens the blow somewhat.

Quarterly estimated payments

You don't pay this once a year. The IRS wants it four times, and skipping payments triggers underpayment penalties even if you pay in full by April.

Notice the periods aren't equal quarters. The second one covers two months, the third covers three.

The safe harbor — how to never owe a penalty

You avoid the underpayment penalty by paying the smaller of:

• 90% of what you'll owe for this year, or
• 100% of what you owed last year — rising to 110% if your prior-year adjusted gross income was over $150,000

The second one is the useful one, because you already know last year's number. Take last year's total tax, divide by four, pay that on each date, and you're protected from penalties regardless of how this year turns out. If you have a monster year, you'll owe more in April — but no penalty.

There's also a de minimis rule: if you'll owe less than $1,000 after credits, no penalty applies at all.

Repairs and tires: pay yourself before the shop does

The mistake isn't failing to budget for repairs. It's budgeting for them as they happen — which means a good stretch feels like profit right up until the bill lands.

The fix is to accrue per mile. Take what a component costs to replace, divide by the miles you expect from it, and set that much aside every mile.

At 10,000 miles a month, a 15-cent maintenance reserve puts $1,500 a month aside. That's a fund that absorbs a turbo or an air conditioning job without touching your income.

Older truck, higher number. A truck past 700,000 miles should be reserving noticeably more than one with 200,000, and if you're not adjusting for that as the truck ages, you're gradually under-reserving without noticing.

The downtime cushion

This is the one people skip, and it's the one that ends businesses.

When the truck is down, revenue goes to zero. Your fixed costs do not. The truck payment, the insurance, the plates, the parking — all of it keeps arriving while you're sitting in a waiting room.

Worse, as covered in the cost per mile guide, a low-mileage month raises the cost of every mile you did run. Downtime hits from both directions at once.

Target two to three months of fixed costs, held separately and not touched. On the example numbers in the cost-per-mile guide — about $4,000 a month fixed — that's $8,000 to $12,000 sitting still.

It feels like dead money right up until the week it's the only reason you still own the truck.

Putting it into practice

The mechanics that actually work, in order of how much they help:

1. A separate business bank account. Non-negotiable. Mixing personal and business money makes your books unreliable and your deductions hard to defend.
2. Separate savings accounts for taxes and for repairs. Two more accounts, moved into on a schedule.
3. Move money when you get paid, not at month end. Every settlement: reserve the tax percentage and the per-mile maintenance amount immediately. What's left is genuinely spendable.
4. Recalculate quarterly. Fuel prices move, insurance renews, the truck ages. A reserve rate set two years ago is describing a different business.

None of this requires software. A spreadsheet and four bank accounts will do it, and plenty of successful owner-operators run exactly that way.

What it does require is knowing your real numbers — net profit, not revenue, and cost per mile across all miles. Which is the part that's genuinely hard to do by hand while also driving eleven hours a day.

This guide is general information, not tax advice. The reserve percentages here are rules of thumb, not a calculation of your liability. Talk to a tax professional about your own situation.

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