Running a small business means juggling a hundred priorities at once, and tax planning often ends up at the bottom of the list — something to think about in March instead of throughout the year. That’s usually where things go wrong. At Martnege Group Accounting PC, we see the same handful of mistakes come up again and again, and almost all of them are avoidable with a little planning ahead of time.
1. Treating Tax Season as a One-Time Event
The biggest mistake we see is business owners who only think about taxes once a year, right before the filing deadline. By the time your return is due, most of the decisions that could have reduced your tax bill — equipment purchases, retirement contributions, entity structure changes — have already passed. Tax planning works best as an ongoing conversation throughout the year, not a scramble in April.
2. Mixing Personal and Business Finances
It’s tempting, especially in the early stages of a business, to run expenses through a personal account or use a business card for the occasional personal purchase. But commingled finances make it harder to track deductible expenses, weaken the liability protection an LLC or corporation is supposed to provide, and are one of the first things that draw scrutiny in an audit. Separate accounts and separate cards aren’t just tidy bookkeeping — they’re protection.
3. Missing Out on Legitimate Deductions
Home office use, vehicle mileage, professional development, retirement plan contributions, health insurance premiums — there’s a long list of deductions business owners routinely leave on the table simply because they didn’t know they qualified, or didn’t keep the documentation to support the claim. This is where working with someone who knows your industry pays for itself many times over.
4. Choosing the Wrong Business Entity — or Never Revisiting the Choice
The entity structure that made sense when you started as a sole proprietor might be costing you money now that you’re generating real revenue. S-corp elections, for example, can offer meaningful payroll tax savings once income reaches a certain level, but plenty of businesses never revisit the decision after their first year. Your entity structure isn’t a “set it and forget it” choice — it’s worth reviewing as your business grows.
5. Waiting Until You Owe Money to Ask for Help
The most expensive tax mistake isn’t any single deduction missed — it’s waiting until there’s a problem to bring in professional support. By the time a notice arrives from the IRS or a return is flagged, the options for reducing what’s owed are far more limited than they would have been with a year of proactive planning behind you.
The Bottom Line
None of these mistakes are complicated to fix, but they do require treating taxes as an ongoing part of running your business, not a once-a-year task. If you’re not sure whether your current approach is costing you money, that’s exactly the kind of question a tax planning conversation is meant to answer.
Martnege Group Accounting PC works with business owners across Southern California to build tax strategies year-round, not just at filing time. If it’s been a while since you’ve had that conversation, we’d be glad to have it with you.