8 Tips for Catching Accounting Mistakes

1. Keep a source document for every transaction
2. Record transactions as they happen

Accounting mistakes are easier to fix when you catch them close to the day they happen. The eight tips below are routine checks: keep a record behind every entry, check that each entry balances, look for balances on the wrong side, reconcile the bank account, run a trial balance and trace any difference, and split the work so one person's error gets a second look. Each check is tied to the open textbook Principles of Accounting, Volume 1: Financial Accounting from OpenStax, opened on October 30, 2026.

This page is about the checks. For mistakes on invoices, see invoicing mistakes to avoid. For the trial balance itself, see what is a trial balance.

1. Keep a source document for every transaction

Every entry should trace back to an invoice, receipt, bank record or contract. OpenStax calls this an original source: a "traceable record of information that contributes to the creation of a business transaction." In its section on internal controls, it says: "An effective internal control system maintains proper documentation, including backups, to trace all transactions."

2. Record transactions as they happen

OpenStax describes transactions being "analyzed, journalized, and posted on a continuous day-to-day basis over the accounting period" before a trial balance is prepared. Entries made weeks later from memory are harder to check against the documents behind them. See what is a journal entry.

3. Check that every entry balances

Under double-entry bookkeeping, OpenStax says the system "requires the sum of the debits to equal the sum of the credits for each transaction." Check each entry before you post it. See what is double-entry bookkeeping.

4. Look for balances on the wrong side

Each type of account has a normal balance. An abnormal balance is an "account balance that is contrary to the expected normal balance of that account." OpenStax gives the example of accounts payable with a debit balance and says: "This situation could possibly occur with an overpayment to a supplier or an error in recording."

5. Reconcile the bank account

OpenStax defines a bank reconciliation as "the internal financial report that explains and documents any differences that may exist between the balance of a checking account as reflected by the bank's records (bank balance) for a company and the company's accounting records (company balance)." The differences it lists include outstanding checks, deposits in transit, bank fees, interest and "Errors initiated by either the client or the bank". For the steps and a worked reconciliation, see what is bank reconciliation.

6. Run a trial balance and trace any difference

If the debit and credit totals don't match, OpenStax says "there is a mistake in at least one of the columns." It describes two checks: divide the difference by two, which can point to an amount entered in the wrong column, or "take the difference between the two totals and divide by nine. If the outcome of the difference is a whole number, then you may have transposed a figure." The sample below uses the second check.

7. Don't treat a balanced trial balance as proof

Equal totals catch some mistakes, not all. OpenStax asks: "If a trial balance is in balance, does this mean that all of the numbers are correct? Not necessarily. We can have errors and still be mathematically in balance." An expense posted to the wrong expense account, for example, leaves both totals unchanged. The bank reconciliation in tip 5 and the documents in tip 1 are how you catch those.

8. Split the work where you can

OpenStax notes that for small businesses, "implementation of internal controls can be a challenge, due to cost constraints, or because a small staff may mean that one manager or owner will have full control over the organization and its operations." Where there's more than one person, it describes separating the asset from the records: "one person within an organization may open an envelope that contains a check, but a different person would enter the check into the organization's accounting system." If you work alone, a bookkeeper or accountant reviewing your reconciliations gives you the second look.

Sample: finding a transposed figure

The business and figures here are a sample, invented for this example.

At month-end, a design studio's trial balance doesn't balance:

Total debits: $18,630.00
Total credits: $18,180.00
Difference: $18,630.00 − $18,180.00 = $450.00

Check 1, divide by two: $450.00 ÷ 2 = $225.00. No account shows $225.00, so a balance in the wrong column isn't the likely cause.

Check 2, divide by nine: $450.00 ÷ 9 = $50.00, a whole number, so the studio looks for a transposed figure on the debit side, which is the higher total.

What it finds: a $270.00 software bill was journalized correctly but posted to Software Expense as $720.00. The digits 2 and 7 were swapped, and $720.00 − $270.00 = $450.00.

After the fix: total debits are $18,630.00 − $450.00 = $18,180.00, equal to total credits. The totals now match, but as tip 7 says, that alone doesn't show every entry is right.

Where Billed fits

Billed's expense tracking page says an expense in Billed "records who you paid, when, how much and which category it belongs to, with the receipt attached to the same entry," and that you can "edit an expense if you entered something wrong." Its financial reporting page says: "See how profitable your business is with Income vs Expense report."

Frequently Asked Questions

How can I catch accounting mistakes early?

Keep a source document for every transaction, record entries as they happen, check that each entry's debits equal its credits, reconcile the bank account, and run a trial balance at month-end.

What does it mean if my trial balance is off by an amount divisible by nine?

OpenStax says that if the difference between the two totals divided by nine is a whole number, "then you may have transposed a figure." In the sample on this page, a $270.00 bill posted as $720.00 made the totals differ by $450.00, and $450.00 ÷ 9 = $50.00.

Does a balanced trial balance mean there are no mistakes?

Not necessarily. OpenStax says: "We can have errors and still be mathematically in balance." An amount posted to the wrong account of the same type leaves the totals equal.

Can a one-person business separate accounting duties?

OpenStax notes that a small staff can make internal controls "a challenge". If you work alone, having a bookkeeper or accountant review your reconciliations adds a second check.

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