Business money and personal money don't mix.

Of all the bookkeeping messes we're hired to clean up, one cause towers over the rest: business and personal money in the same accounts. It's also the cheapest problem to fix — about one afternoon of setup.

What commingling actually costs

• Missed deductions. Business expenses buried in a personal account don't get counted. You pay tax on income those expenses should have offset.
• Bookkeeping that costs double. Every mixed account means someone examining each transaction and asking "was this business?" — billable time spent sorting instead of reporting.
• A weaker liability shield. If you have an LLC or corporation, mixing funds is a classic argument for piercing the corporate veil — treating your personal assets as the business's. The separation is a large part of why the entity exists.
• Audit pain. Defending deductions from a mixed account means handing over personal financial life alongside business records.

The one-afternoon fix

• Open a business checking account — and a business credit card, or at minimum a card used exclusively for business.
• Move every recurring business charge — software, subscriptions, insurance, phone — onto the business accounts. Fifteen minutes of updating payment methods.
• Route all income to the business account. Update payment processors, invoicing tools, and anywhere clients pay you.
• Pay yourself on purpose. A regular transfer from business to personal — weekly or monthly. That transfer is your paycheck; personal spending happens on the personal side only.

When you slip (you will)

Swiped the wrong card at the hardware store? Don't try to bury it, and don't "pay it back" informally. Record it for what it is: a personal expense paid from the business is an owner draw; a business expense paid from a personal account is an owner contribution (keep that receipt — it's still deductible). Categorized honestly, slips are a non-event. Hidden, they compound.