4.1 Where Bookkeeping Errors Occur & How to Find Them

Why error detection is a Certified Bookkeeper skill

The American Institute of Professional Bookkeepers (AIPB) Certified Bookkeeper (CB) credential tests error correction on Part 1, Test 2, a one-hour Prometric sitting that also covers bank reconciliation. AIPB scores that test separately from the adjusting-entries hour in the same appointment; the published passing grade is 75% on each test. AIPB's Mastering Correction of Accounting Errors skill list is concrete: find and correct errors in the general ledger, complete the monthly bank reconciliation and record the related journal entries, use the trial balance to find bookkeeping and accounting errors, and correct current-period accrual and deferral errors.

This OpenExamPrep chapter is independent study material for those skills. It is not an AIPB publication and does not claim official approval, review, or partnership. Sections 4.1–4.3 teach error types, trial-balance diagnostics, and the bank rec. Current-period accrual and deferral corrections are Chapter 5 of this guide. Keep the bank reconciliation in your study path—Test 2 will mix rec items with error-type items in the same hour, and skipping Section 4.3 to jump to accruals is a common way to leave cash unproved.

A trial balance that footed last month is not a guarantee this month. Errors enter from tired posting, a vendor invoice entered twice, a decimal that slid, or two mistakes that cancel. Your job on the exam—and in a firm of up to 100 employees, the size AIPB cites for the credential—is to classify the error, find it with a method rather than a scavenger hunt, and record a correcting entry that does not create a new mistake.

Original entries, reversing entries, and correcting entries

Name the entry family before you open the general journal. The exam will give you a story and ask which entry is appropriate. Mixing these three families is one of the highest-frequency Test 2 traps.

An original entry is the first recording of a transaction in a journal, then posted to the ledgers. If the original is wrong—wrong account, wrong amount, wrong side, or omitted—every report that uses those accounts is wrong until a correction posts.

A reversing entry is an optional entry dated the first day of the next accounting period that swaps the debit and credit of a prior adjusting entry. Its purpose is workflow, not error repair. Example: May 31 accrued wages of $1,800 (debit Wages Expense $1,800, credit Wages Payable $1,800). On June 1 you may reverse (debit Wages Payable $1,800, credit Wages Expense $1,800). When the June 5 payroll check for $4,500 is recorded, the full $4,500 can debit Wages Expense. June's net wage expense is then $4,500 − $1,800 = $2,700, which is the June-period portion if the $4,500 check covers the $1,800 May accrual plus $2,700 of June wages. Reversing a correct accrual does not fix anything. You do not reverse a random cash purchase, and you do not reverse a correcting entry as a matter of routine.

A correcting entry is posted because something already in the books is wrong. You may use a two-step method (reverse the entire wrong original, then record the correct original) or a one-step method (post only the net change to the accounts that are still wrong). Prefer one-step when Cash, or another account that was already correct, must not be touched again—especially after the check has cleared the bank.

Worked one-step correction (Cash already correct)

On April 12 the firm bought $860 of office supplies for cash and posted debit Supplies Expense $860, credit Cash $860. Supplies should have been an asset. Cash is already correct.

Do not credit Cash a second time. A two-step that reversed the original (debit Cash $860, credit Supplies Expense $860) and then re-recorded the purchase (debit Supplies $860, credit Cash $860) nets to the same accounts, but it churns Cash after the bank has already paid the $860 and it invites a double-count if anyone posts only half of the pair.

Worked two-step correction (both sides wrong)

A $1,400 cash sale was posted debit Accounts Receivable $1,400, credit Sales $1,400.

Net: Accounts Receivable is cleared, Cash increases $1,400, Sales remains $1,400. The two-step is easier to follow when every original line was wrong.

Worked one-step amount correction

Rent of $640 cash was recorded as $460 on both sides (a transposition copied to debit and credit). Cash was not credited enough, so Cash is overstated $180; Rent Expense is understated $180.

Scratch three lines before you journalize: (1) what was recorded, (2) what should have been recorded, (3) which accounts are already correct. That scratch is how you choose one-step versus two-step.

Where errors hide

Hunt in this order after you know the trial-balance difference (the search math is Section 4.2):

1. Source documents — vendor invoices, customer invoices, check stubs, deposit slips, ACH notices, credit memos, packing slips. A missing invoice number, a duplicate bill, or a stub that does not match the canceled check starts an error before the journal is open.
2. Journals — general journal and special journals (sales, cash receipts, cash disbursements, purchases). Wrong account title, wrong amount, omitted line, extra line, or a special-journal column total that does not equal the detail.
3. Posting — copying a journal line into the wrong ledger account, the wrong side, twice, or not at all. Control-account versus subsidiary-ledger mismatches live here.
4. Footing — adding a journal column, a ledger account, or the trial-balance columns incorrectly. A $1, $10, or $100 difference is often addition, not a mysterious missing invoice.

Special journals deserve a CB-level note. In a cash disbursements journal, the Cash credit total, Accounts Payable debit total, Purchases-discount credit total, and Other Accounts debit column must each foot and cross-foot. If Other Accounts posts as individual lines to the ledgers but the Cash total posts as one figure, a misfooted Cash column throws the trial balance off while the Other Accounts ledgers look fine. Re-foot the special journal before you tear apart every subsidiary ledger.

Error categories the exam expects you to name

Error of omission. The transaction was never journalized. Debit and credit are both missing. The trial balance still balances. Cash omissions often surface on the bank rec (Section 4.3). Noncash omissions—a credit sale never recorded—surface from invoice-number gaps, customer statements, or a shipping log. Example: invoice 4418 for $975 on account never entered. Accounts Receivable and Sales are both $975 low. The equality test is silent.

Error of commission. Entered, but to the wrong account of a similar type. Debit Shop Supplies Expense $210 instead of Warehouse Supplies Expense $210. The trial balance balances. Department reports are wrong; total expenses may still be right.

Error of principle. Wrong accounting treatment: expense versus asset, revenue versus liability, drawing versus expense. Debit Repairs Expense $4,200 for a new computer that should be Equipment. Equal debits and credits were recorded, so the trial balance balances, but net income is understated $4,200 before depreciation and assets are understated the same amount. Owners care about this error because profit is wrong even though the trial balance "proved."

Transposition. Two digits swapped. $2,340 posted as $2,430. Difference $90; $90 ÷ 9 = 10. A number and its digit-swap differ by a multiple of 9. Screening test when the trial balance is out of balance: if the difference ÷ 9 is a whole number, scan for swapped digits. Why 9? Swapping digits in the tens and ones places changes the value by 9 times the digit difference (72 versus 27 differs by 45 = 9 × 5). Swapping hundreds and tens is 90 times the digit difference, still a multiple of 9. Worked: $7,182 recorded as $7,812. Difference $630; $630 ÷ 9 = 70. Look for an 18/81 swap or for $7,182 on the source document.

Slide. Decimal or place-value shift. $450 recorded as $4,500 (left one place) or as $45.00 (right one place). A one-place slide difference equals 9 times the smaller amount, so it is divisible by 9, and the quotient often equals that smaller amount. Left slide: $360 posted as $3,600. Difference $3,240; $3,240 ÷ 9 = $360. Search ledgers for $3,600 that should be $360. Right slide: $1,260 posted as $126. Difference $1,134; $1,134 ÷ 9 = $126. Search for a $126 posting. Two-place left slide of $360 to $36,000: difference $35,640 = $360 × 99, still divisible by 9, but the quotient $3,960 does not equal $360. The 9-test still flags it; matching the quotient to a ledger amount is weaker.

Compensating errors. Two mistakes of equal amount that offset on the trial balance. Posted an extra $180 debit to Insurance Expense and an extra $180 credit to Service Revenue. Debits still equal credits. Both accounts are wrong; net income might even look reasonable because extra expense and extra revenue cancel. Detection requires account-by-account review, not the equality test.

Equal wrong amount on both sides. Invoice $404 journalized as $440 to Supplies and Accounts Payable. The trial balance balances. The $36 transposition never appears as a trial-balance difference because both columns moved together. Pull the source document.

One-sided posting and side flips. Posted the debit only, or listed a debit balance in the credit column of the trial balance. These throw the trial balance out of balance. Section 4.2 is the search sequence: re-foot, look for the difference, divide by 2, divide by 9.

Exam habits

Do not start a correcting entry until you can state what was recorded, what should have been recorded, and which accounts are already correct. If the difference you are chasing is a cash amount, finish the bank reconciliation (Section 4.3) before you rewrite half the expense ledger. NSF checks, EFT drafts, and book errors in the cash account look like mystery cash until they sit on the rec.

Accrual and deferral mistakes—failed to accrue interest, prepaid rent sitting in expense, unearned fees recognized too early—are Chapter 5. They often leave the trial balance in balance. Mention them so you do not think Test 2 is only bank rec, then return to the rec and the trial-balance diagnostics rather than skipping cash.