Small business owners often focus on the obvious write-offs—rent, payroll, software, and supplies—but some of the most valuable deductions are the ones that get missed. In 2025, that can mean paying more tax than necessary or creating avoidable problems if your records do not support what you claim. The Internal Revenue Code generally allows deductions for ordinary and necessary business expenses under, and the IRS expects businesses to keep records that clearly show income and expenses.
Below are seven deductions that small business owners commonly overlook.
1. The business use of your home
Many owners avoid this deduction because they assume it is risky or too complicated. But if part of your home is used exclusively and regularly for business, it may qualify. The space must generally be your principal place of business, a place where you meet clients or customers, or a separate structure used for business.
The IRS recognizes both:
- the regular method, which allocates actual home expenses between business and personal use; and
- a simplified method, which can reduce the recordkeeping burden.
This deduction is often missed by:
- sole proprietors working from home,
- consultants and freelancers,
- owners doing administrative work from a home office even if they also work elsewhere.
The key issue is substantiation. If you claim it, keep records showing the square footage and the business purpose of the space.
2. Vehicle expenses, especially when business use is only partial
Business owners often either fail to deduct vehicle costs at all or deduct them incorrectly. If you use a car, van, pickup, or panel truck for business, you may generally deduct either:
- actual expenses, or
- the standard mileage rate.
For 2025, the business standard mileage rate is 70 cents per mile.
This deduction is commonly overlooked when:
- the vehicle is used for both personal and business purposes,
- the owner assumes mixed use makes the deduction unavailable,
- mileage logs were not maintained consistently.
The IRS sources emphasize that only the business-use portion is deductible, so contemporaneous mileage records matter.
3. Startup costs and organizational costs
New business owners frequently miss these because they assume pre-opening costs are either fully deductible immediately or not deductible at all. The actual rule is more nuanced.
Business startup costs are generally capital expenditures, but a taxpayer may elect to deduct up to $5,000 of startup costs and up to $5,000 of organizational costs, subject to phaseout once total costs exceed $50,000. Any remaining amount generally must be amortized.
These costs can include amounts paid before the business begins operations, such as:
- advertising before launch,
- travel to line up vendors or customers,
- market surveys,
- training.
This deduction is especially important for businesses that began recently or incurred substantial pre-opening costs in 2025.
4. Self-employed health insurance
Owners often miss this because they look for it among itemized deductions, when it is generally claimed as an adjustment to income instead. If you are self-employed, you may generally deduct amounts paid for medical, dental, and qualified long-term care insurance for yourself, your spouse, dependents, and certain children under age 27, subject to the applicable limits.
This deduction is commonly overlooked by:
- sole proprietors,
- partners,
- S corporation owners who do not coordinate payroll reporting correctly.
The deduction is not unlimited, and eligibility can be affected if you or your spouse are eligible for subsidized employer coverage.
5. Interest and loan-related costs
Business owners usually remember to deduct obvious loan interest, but they often miss related financing costs or fail to allocate interest correctly when borrowed funds are used for mixed purposes.
IRS guidance in the sources confirms:
- business interest may be deductible, subject to applicable limitations.
- loan expenses such as legal fees and commissions paid to obtain a business loan are generally not deducted all at once but are prorated over the term of the loan.
- if loan proceeds are used for more than one purpose, interest must be allocated by use of proceeds.
This is often missed when owners:
- refinance debt,
- use one line of credit for both business and personal spending,
- pay financing fees at closing and forget them later.
6. Depreciation, and special depreciation allowances
This is less a single deduction than a category of deductions that are often underclaimed. When a business buys equipment, furniture, computers, machinery, or certain improvements, the owner may not be limited to deducting the cost slowly over many years.
For 2025, the sources indicate:
- the maximum deduction increased to $2,500,000, with phaseout beginning when qualifying property placed in service exceeds $4,000,000.
- 100% bonus depreciation was restored for certain qualified property acquired and placed in service after January 19, 2025.
- qualified production property may also be eligible for a 100% special depreciation allowance if placed in service after July 4, 2025.
These deductions are often overlooked because owners:
- expense the wrong amount,
- fail to elect,
- do not realize used property may qualify in some cases,
- assume depreciation is automatic without filing the proper forms.
The IRS sources also stress that depreciation must be tracked carefully because basis must be adjusted for depreciation allowed or allowable.
7. Record-supported “small” expenses that add up
A surprising amount of deductible spending gets lost simply because it is scattered across the year. IRS guidance recognizes many ordinary and necessary business expenses that owners often fail to capture, including:
- accounting fees,
- tax preparation fees allocable to the business,
- business-related telephone charges,
- postage,
- subscriptions to professional or trade publications,
- small tools,
- utilities,
- advertising.
These are often missed because:
- they are paid from personal accounts,
- receipts are not retained,
- they are not coded correctly in the books,
- they seem too minor individually.
The tax law does not require a deduction to be large to be valid. But it does require records. The IRS expects supporting documents such as invoices, receipts, canceled checks, and account statements to support deductions.
A few 2025-specific cautions
A deduction is only useful if it is claimed correctly. A few points from the sources are especially important in 2025:
- Business meals generally reverted to the 50% deduction rule; the temporary 100% restaurant deduction has expired.
- Excess business loss limitations for noncorporate taxpayers were made permanent beginning in later years under the 2025 legislation, and the sources note the rule’s continuing importance in NOL calculations.
- Good recordkeeping remains foundational. The IRS requires taxpayers to keep records sufficient to establish income, deductions, and credits.
Final thought
The most overlooked deductions are usually not exotic tax strategies. They are ordinary deductions that business owners either do not know about, do not track, or do not document well enough to claim. In 2025, the biggest missed opportunities for many small businesses are likely to be:
- home office expenses,
- vehicle costs,
- startup and organizational costs,
- self-employed health insurance,
- financing costs,
- depreciation-related deductions,
- and accumulated small operating expenses
