6 Business Mistakes I’d Never Make as an Accountant
Running a business is exciting, but it’s also full of pitfalls that can quietly cost you money, time, and peace of mind.
At Rhombus Accounting, we’ve seen hundreds of small business owners make the same financial mistakes, often without realising how damaging they can be. The good news? They’re all preventable.
Here are the six business mistakes I’d never make as an accountant, and what you can do instead to keep your finances (and sanity) in check.
1. Mixing Personal and Business Finances
That “quick” personal purchase on the business card might not feel like a big deal, but it creates chaos in your books.
When personal and business expenses get mixed together, it makes bookkeeping messy, tax returns more complicated, and your accounts less reliable. You’ll end up wasting hours (and probably paying your accountant extra) trying to sort through it all later.
The fix:
Open a dedicated business bank account and never use it for personal spending. It keeps your records clean, your accountant happy, and your year-end far simpler.
2. Not Saving for Tax Throughout the Year
Too many business owners treat tax like a surprise bill, and it always comes at the worst time.
If you don’t set money aside regularly, you’ll find yourself scrambling to cover your tax bill when it’s due. It’s one of the most common reasons for cash flow stress.
The fix:
Create a “tax pot.” Every month, transfer a percentage of your income (typically 20 to 25 percent) into a separate account. That way, when HMRC comes knocking, you’re already prepared.
It’s simple but it works, and it saves you from sleepless nights when payment deadlines roll around.
3. Not Checking If Expenses Are Actually Deductible
Just because something feels like a business expense doesn’t mean HMRC agrees.
We’ve seen businesses claim things that don’t qualify, from home décor to personal clothing, only to face questions later. On the flip side, some owners miss out on legitimate deductions because they’re unsure what’s allowed.
The fix:
Learn the basics of allowable expenses or work with an accountant who’ll review your spending and help you claim everything you’re entitled to without overstepping the rules.
A clear understanding of what counts as deductible can save you hundreds or even thousands each year.
4. Ignoring the Numbers
Your profit and loss statement tells a story. It shows where your business is healthy, where it’s leaking money, and where opportunities are waiting.
Too often, business owners don’t look at their numbers until it’s too late. By then, margins have shrunk, costs have crept up, and cash flow is tight.
The fix:
Check your financial reports monthly. Track sales trends, overheads, and profit margins. Even if you’re not a numbers person, reviewing your accounts regularly gives you control and confidence in your decisions.
5. Winging It With Pricing
Pricing is one of the most common areas where business owners go wrong. Undercharging might win you a few clients in the short term, but it’s the fastest route to burnout.
If your prices don’t reflect your costs, skills, and market value, you’ll end up working harder for less.
The fix:
Know your margins. Calculate the cost of delivering your product or service, then build your price around profit, not guesswork. A small pricing adjustment today can make a huge difference to your income over the year.
6. Waiting Until Year-End to Get Financial Advice
If you only talk to your accountant at year-end, you’re missing out on the real value of good financial planning.
By the time the books are closed, it’s too late to make tax-saving decisions or strategic changes.
The fix:
Schedule check-ins with your accountant throughout the year. At Rhombus, we help clients plan ahead, forecast cash flow, and find tax efficiencies before deadlines hit. That’s where the real savings happen.
The Bottom Line
Good financial habits don’t just save money, they build stability, reduce stress, and help your business grow sustainably.
Start with these simple steps:
Keep business and personal finances separate
Save for tax every month
Understand what you can and can’t claim
Stay close to your numbers
Price confidently
Get proactive financial advice before it’s too late
If you follow these principles, you’ll avoid the mistakes that hold so many business owners back and set yourself up for long-term success.
Meet Lewis
Lewis is a professional accountant and founder of Rhombus Accounting. He regularly shares his knowledge and best advice here on his blog and on other channels such as LinkedIn.
Book a call today to learn more about what Lewis and Rhombus Accounting can do for you.
