The average small business owner misses between $5,000 and $10,000 in legitimate deductions every year. That is not because the tax code is deliberately hiding these write-offs; it is because most business owners are too busy running their companies to track every eligible expense. According to Forbes, an estimated 93% of businesses leave money on the table at tax time.
The problem got worse in 2026, but not in the way you might expect. The One Big Beautiful Bill Act (OBBBA), signed into law on July 4, 2025, actually made this the most deduction-friendly tax year in nearly a decade. It permanently restored 100% bonus depreciation, raised the Section 179 deduction limit to $2.5 million, and increased the Qualified Business Income (QBI) deduction from 20% to 23%. Yet most business owners are not aware of these changes, which means even more savings are being left behind.
This article focuses on five specific deductions that small business owners miss most frequently.
1. The Home Office Deduction
If you use part of your home regularly and exclusively for business, you can deduct a portion of your rent or mortgage interest, utilities, insurance, and repairs. The IRS offers two calculation methods, and choosing the right one can mean the difference between a $1,000 deduction and a $4,800+ deduction.
Why Business Owners Miss It
Many small business owners avoid claiming the home office deduction because they fear it will trigger an IRS audit. This concern is largely outdated. The IRS provides detailed guidance on this deduction, and it is entirely legitimate when you meet the “regular and exclusive use” standard. The real reason most people miss it is that they either do not know about both calculation methods or they default to the easier one without comparing.
2. Self-Employed Health Insurance Premiums
Self-employed business owners can deduct 100% of health insurance premiums paid for themselves, their spouse, and their dependents. This includes medical, dental, and long-term care insurance. It is an above-the-line deduction, meaning you get it even if you do not itemize.
Why Business Owners Miss It
This deduction is missed for two main reasons. First, many self-employed people simply do not realize they qualify—they associate health insurance deductions with employer-provided plans. Second, and more critically for S-Corp owners, the insurance must be paid through the business and reported in Box 1 of your W-2. If the premium comes out of your personal account without being routed through the business, your CPA cannot claim it. This structural mistake costs S-Corp owners thousands every year.
3. The Qualified Business Income (QBI) Deduction — Now 23%
Pass-through business owners (sole proprietors, S-Corps, partnerships, LLCs) can deduct up to 23% of their qualified business income for tax years beginning after December 31, 2025. The OBBBA made this deduction permanent and increased it from the previous 20% rate.
What Changed Under OBBBA in 2026
The QBI deduction under Section 199A was originally scheduled to expire at the end of 2025. The OBBBA not only made it permanent but also improved it in three important ways: the deduction rate increased from 20% to 23%, the income thresholds for specified service trades and businesses (SSTBs) were expanded so more business owners qualify for the full deduction, and a new minimum deduction of $400 was introduced for anyone with at least $1,000 in qualified business income.
Why Business Owners Miss It
The QBI deduction is complex, and many business owners either do not know it exists or assume their CPA is already claiming it. The truth is that proper entity structure, reasonable compensation planning (for S-Corps), and income threshold management can significantly affect how much of this deduction you actually receive. Business owners in specified service trades (law, medicine, consulting, accounting) often assume they are automatically disqualified, when in reality the expanded OBBBA thresholds may now allow them to claim all or part of it.
4. Startup Costs (Section 195)
Businesses can deduct up to $5,000 in startup costs in their first year of operation under Section 195. Qualifying expenses include market research, employee training, advertising before launch, travel to secure suppliers, and professional fees for setting up the business. The $5,000 deduction phases out dollar-for-dollar once total startup costs exceed $50,000.
Why Business Owners Miss It
New business owners often fail to track expenses that occur before the business officially opens. That website you built two months before launch, the legal fees to form your LLC, the industry conference you attended while researching your market—all of these are potentially deductible startup costs. The other common mistake is attempting to deduct all startup costs in the first year when total costs exceed $5,000. Amounts above the initial $5,000 deduction must be amortized over 180 months (15 years).
Important: The startup deduction only applies to businesses that actually begin operating. If you investigate starting a business but never launch, those investigatory costs are not deductible.
5. Equipment and Asset Purchases (Section 179 + Bonus Depreciation)
In 2026, the OBBBA permanently restored 100% bonus depreciation and raised the Section 179 deduction limit to $2.5 million. This means you can deduct the full purchase price of qualifying equipment, vehicles, software, and other business assets in the year you buy them—instead of spreading the deduction over multiple years.
What Changed Under OBBBA in 2026
Before the OBBBA, bonus depreciation was phasing down: 60% for 2024, 40% for 2025, and 20% for 2026 before expiring entirely. The OBBBA reversed this decline and permanently locked in 100% bonus depreciation. It also raised the Section 179 limit from $1.16 million to $2.5 million, with the phase-out threshold increasing to $4 million. For most small businesses, this means any qualifying asset purchase can be fully deducted in the year of purchase.
Why Business Owners Miss It
Many business owners are unaware that bonus depreciation was restored, or they confuse Section 179 with bonus depreciation and assume they have to pick one. In reality, you can combine both methods for maximum first-year deductions. Additionally, some owners do not realize that qualifying assets include not just heavy equipment but also computers, office furniture, software, certain vehicle types, and even some building improvements.
Bonus: 3 More Deductions That Fly Under the Radar
Bank and credit card fees: Monthly service charges, transaction fees, the cost of ordering business checks, and interest on business credit cards and loans are all deductible. Review your bank statements at year-end—these small charges accumulate into a meaningful write-off.
Professional development and education: Costs for courses, conferences, workshops, and certifications that improve your skills in your current business are fully deductible. This includes online courses, trade publications, and membership dues for professional organizations.
Software subscriptions and digital tools: Accounting software, project management platforms, cloud storage, CRM tools, and industry-specific apps are all deductible business expenses. Many owners pay for these through personal accounts and forget to claim them.
Step 1: Separate business and personal finances:
Open a dedicated business bank account and credit card. Commingling funds makes it nearly impossible to defend deductions in an audit and dramatically increases the chance your CPA misses legitimate write-offs.
Step 3: Review IRS updates annually:
Tax law changes every year. The OBBBA alone introduced multiple deduction changes for 2026. Set a calendar reminder to review updates each January, or work with a CPA who proactively communicates changes.
Step 2: Track expenses in real time:
Use accounting software that categorizes expenses as they happen. Trying to reconstruct a full year of expenses during tax season is how deductions get missed. Mobile apps that capture receipts via photo make this nearly effortless.
Step 4: Make quarterly estimated payments:
If you expect to owe more than $1,000 in federal taxes for 2026, you are required to make quarterly estimated payments. Missing these triggers penalties regardless of how much you overpay at filing time.