Most small business owners leave between $5,000 and $10,000 in legitimate deductions unclaimed every year — not because the tax code hides these write-offs, but because running a business leaves little time to track every eligible expense.
2026 is shaping up to be one of the most deduction-friendly tax years in recent memory, thanks to the One Big Beautiful Bill Act (OBBBA), signed into law on July 4, 2025. The legislation permanently restored 100% bonus depreciation, raised the Section 179 deduction limit to $2.5 million, and made the Qualified Business Income (QBI) deduction permanent at 20% — with an increase to 23% taking effect starting in the 2026 tax year. Most small business owners aren’t aware of these changes, which means even more savings are being left on the table.
Below are five deductions that small business owners miss most often.
1. The Home Office Deduction
If you use part of your home regularly and exclusively for business, you can deduct a proportional share of your rent or mortgage interest, utilities, insurance, and repairs. The IRS offers two calculation methods — and picking the right one can be worth thousands of dollars.
Why Business Owners Miss It
The most common reason small business owners skip this deduction is fear of an audit. That concern is largely outdated. The home office deduction is well-established in the tax code, fully legitimate when you meet the “regular and exclusive use” standard, and supported by detailed IRS guidance. The real issue is that most owners either don’t know both calculation methods exist, or they default to the simpler one without ever running the numbers on the alternative.
The two methods are the Simplified Method, which allows a flat $5 per square foot up to 300 square feet (maximum $1,500), and the Regular Method, which calculates the actual percentage of your home used for business and applies it to real expenses. Depending on your home’s size and costs, the Regular Method can yield $4,800 or more — making the comparison worth the extra effort.
S-Corp owners, take note: If you operate as an S-Corp, you cannot claim the home office deduction directly on your personal return. Instead, you need to establish an accountable plan that allows your S-Corp to reimburse you for those expenses. Without this structure in place, the deduction disappears entirely — and it’s one of the most common oversights among S-Corp owners.
2. Self-Employed Health Insurance Premiums
If you’re self-employed, you can deduct 100% of health insurance premiums paid for yourself, your spouse, and your dependents — including medical, dental, and long-term care coverage. Because it’s an above-the-line deduction, you receive it regardless of whether you itemize.
Why Business Owners Miss It
Two problems account for most missed claims here. The first is a simple awareness gap: many self-employed owners associate health insurance deductions with employer-provided plans and don’t realize they qualify on their own. The second is a structural mistake that quietly costs S-Corp owners thousands of dollars every year.
If you operate as an S-Corp, the premiums must be paid through the business and reported in Box 1 of your W-2. Paying from your personal account — even for a legitimate business expense — breaks the chain. Without that paper trail, your CPA has no basis to claim the deduction, and the savings vanish. It’s a procedural requirement that’s easy to overlook and expensive to get wrong.
3. The Qualified Business Income (QBI) Deduction — Now 23%
If you own a pass-through business — sole proprietorship, S-Corp, partnership, or LLC — you can now deduct up to 23% of your qualified business income. This applies to tax years beginning after December 31, 2025, and the deduction is now permanent.
What Changed Under OBBBA in 2026
Before the OBBBA, the QBI deduction under Section 199A was set to expire at the end of 2025. The new law not only preserved it but strengthened it in three ways. The deduction rate increased from 20% to 23%. The income thresholds for specified service trades and businesses (SSTBs) were expanded, meaning more owners can now qualify for the full deduction. And a new $400 minimum deduction was introduced for any taxpayer with at least $1,000 in qualified business income — a small but meaningful floor that didn’t exist before.
Why Business Owners Miss It
The QBI deduction is one of the most valuable in the tax code and one of the most frequently underutilized. Some owners don’t know it exists. Others assume their CPA is already maximizing it. But how much you actually receive depends heavily on factors your CPA needs your help with — your entity structure, how you handle reasonable compensation as an S-Corp owner, and how your income sits relative to the thresholds.
Owners in specified service trades — law, medicine, consulting, accounting — often assume they’re automatically disqualified and never ask the question. Under the expanded OBBBA thresholds, some of them now qualify for all or part of the deduction. If you’re in a service business and haven’t reviewed this recently, it’s worth a conversation with your tax advisor.
4. Startup Costs (Section 195)
Under Section 195, new businesses can deduct up to $5,000 in startup costs during their first year of operation. Qualifying expenses include market research, pre-launch advertising, employee training, travel to secure suppliers, and professional fees for business formation. The $5,000 deduction phases out dollar-for-dollar once total startup costs exceed $50,000, and any amount above the initial deduction must be amortized over 180 months (15 years).
Why Business Owners Miss It
The most common mistake is failing to track expenses that happen before the business officially opens. The website you built two months before launch, the legal fees to form your LLC, the industry conference you attended while scoping out the market — these are all potentially deductible startup costs that most new owners never think to record.
The second mistake runs in the opposite direction: assuming all startup costs can be written off in year one. Once your total startup costs exceed $5,000, the remainder doesn’t disappear — it gets amortized over 15 years. Trying to deduct it all at once is an error that can trigger corrections and penalties.
One Important Limitation
The startup deduction only applies to businesses that actually begin operating. If you research and investigate launching a business but never open, those investigatory costs are not deductible. The deduction rewards action, not intention.
5. Equipment and Asset Purchases (Section 179 + Bonus Depreciation)
The OBBBA made 2026 one of the best years on record to purchase business assets. Between permanently restored 100% bonus depreciation and a Section 179 deduction limit raised to $2.5 million, most small businesses can now deduct the full purchase price of qualifying equipment, vehicles, software, and other assets in the year they buy them — no spreading the deduction across multiple years required.
What Changed Under OBBBA in 2026
Before the OBBBA, bonus depreciation was on a scheduled decline: 60% in 2024, 40% in 2025, and 20% in 2026 before disappearing entirely. The new law reversed that trajectory and made 100% bonus depreciation permanent for qualifying property acquired and placed in service after January 19, 2025. At the same time, the Section 179 expensing limit rose from $1.25 million to $2.5 million, with the phase-out threshold increasing from $3.13 million to $4 million. For most small businesses, any qualifying asset purchase made this year can be fully deducted the same year.
Why Business Owners Miss It
Awareness is the first obstacle — many owners simply don’t know bonus depreciation was restored and are still operating under the assumption that equipment costs have to be depreciated gradually. The second obstacle is confusion between the two methods. Section 179 and bonus depreciation are not an either/or choice; they can be combined to maximize first-year deductions, with Section 179 applied first to assets where selective expensing is useful, and bonus depreciation applied to the rest.
The third oversight is a narrow view of what qualifies. Eligible assets go well beyond heavy machinery. Computers, office furniture, off-the-shelf software, certain vehicles, and qualifying building improvements all count. If you’ve purchased any of these in 2025 or 2026 without claiming full expensing, there may be deductions sitting unclaimed on your return.
Bonus: 3 More Deductions That Fly Under the Radar
Bank and credit card fees: Monthly service charges, transaction fees, business check orders, and interest on business credit cards and loans are all fully deductible. These charges tend to feel too small to bother with, but they add up across a full year. A quick review of your bank and credit card statements at year-end often turns a handful of overlooked line items into a meaningful write-off.
Professional development and education: Courses, conferences, workshops, and certifications that improve your skills in your current business are fully deductible — including online courses, trade publications, and professional organization dues. The key requirement is that the education relates to your existing business, not a career change or new field. If you’re investing in yourself to do your current work better, the IRS generally allows it.
Software subscriptions and digital tools: Accounting software, project management platforms, cloud storage, CRM tools, and industry-specific apps all qualify as deductible business expenses. The reason so many owners miss these is simple: the subscriptions run through a personal credit card or email address and never make it into the business records. A one-time audit of your recurring charges — personal accounts included — often surfaces several hundred dollars in forgotten deductions.
Step 1: Separate business and personal finances:
Open a dedicated business bank account and credit card and keep them strictly separate. Commingling funds makes it nearly impossible to defend deductions in an audit and dramatically increases the chance that legitimate write-offs get missed — by you or your CPA.
Step 3: Make quarterly estimated payments:
If you expect to owe more than $1,000 in federal taxes for the year, you are required to make quarterly estimated payments. Missing them triggers penalties regardless of how much you ultimately pay at filing — so the habit of paying quarterly protects you even in a good year.
Step 2: Track expenses in real time:
Use accounting software that categorizes expenses as they occur rather than trying to reconstruct a full year of spending during tax season. Most modern platforms include mobile apps that capture receipts by photo, which makes the habit nearly effortless to maintain.
Step 4: Review tax law changes every January:
Tax law changes annually, and major legislation like the OBBBA can shift your deduction strategy significantly from one year to the next. Set a calendar reminder each January to review updates, or work with a CPA who communicates changes to you proactively rather than waiting for you to ask.