Nobody sets out to run the business through a personal card. It happens once when the business card is at home, then again at a supplier who only takes cash, and by the end of the year the books depend on somebody remembering which groceries were for the staff room.
What mixing actually costs
- Time. Every mixed statement has to be read line by line by someone who can tell the difference. That is the single biggest driver of a bookkeeping bill.
- Accuracy. Decisions made from memory months later are guesses, and guesses land in the numbers you price and plan from.
- Evidence. If a deduction is ever questioned, a clean business account is the record. A mixed account is an argument.
- Separation. For an LLC or corporation, consistently running personal spending through the company is the kind of fact that gets raised when someone challenges the separation between you and the entity. Whether that matters in your situation is a question for your attorney — but the bookkeeping habit is what creates the fact pattern.
The setup
A business checking account, one business card, and a standing rule that both are used for nothing else. Pay yourself on a schedule — a transfer to your personal account on the same day each month — so personal spending happens from personal money. Most of the mess disappears with that one change.
Recording owner money
Money you take out is not an expense, and money you put in is not income. In the books, a draw (or distribution) reduces owner's equity and a contribution increases it. If you're taxed as an S corporation, reasonable compensation has to run through payroll, and how much is a question for your CPA — but whatever they set, the books have to record it as payroll rather than as a draw.
When it happens anyway
- Business expense on a personal card. Reimburse yourself from the business with a reference to the receipt, or record it as an owner contribution plus the expense. Don't leave it invisible.
- Personal expense on the business card. Code it to owner draw, not to a plausible-looking expense account. Miscoding it is the part that causes problems later.
- Shared costs — a phone, a vehicle, part of a home — are documented as they are incurred (mileage log, usage split) and the deductible portion is your CPA's call at year end. The bookkeeping job is to have the record, not to decide the percentage.
Fixing history
Do not try to recategorize three years of mixed statements. Pick a clean start date — the beginning of a month or a quarter — open the accounts, and run cleanly from there. For prior periods, do enough to make them defensible and hand the judgment calls to your CPA. A cleanup that never ends is worse than a clean line drawn and kept.
Once the accounts are separate, the rest of the routine gets short. See the monthly close.
