The trial balance

Every account, netted onto one side, with both columns summed. It proves the arithmetic, and you need to know exactly how much it does not prove.

Reading: 10 min
Teaches: 5
Sources: 2

Net each account onto its own side, list them all, and sum the two columns. If double-entry was obeyed, the totals are identical — not close, identical. That is the trial balance, and it is the first thing an accountant looks at every month. It is a working paper, not a financial statement: it is never published, and outside the finance team only the auditors ever see one.

01Something happens
02Journal
03Ledger
04Trial balanceEvery account, netted, proved.
05Adjust
06Statements
07Close

Unadjusted trial balanceNorthwind Traders, Inc. · as at 30 September 2026 · USD · Accrual
Account	Name	Debit	Credit
1000	Cash — operating	32,900.00
1200	Accounts receivable	8,000.00
1300	Inventory	1,000.00
1400	Prepaid insurance	7,200.00
1500	Vehicles	24,000.00
2000	Accounts payable		6,000.00
2400	Deferred revenue		3,000.00
3000	Common stock		60,000.00
4000	Revenue		31,500.00
5000	Cost of revenue	17,000.00
6000	Payroll expense	8,400.00
6200	Rent expense	2,000.00
Total		100,500.00	100,500.00

Debits equal credits at 100,500.00. The arithmetic is proved; nothing else is.

Northwind at 30 September, before adjustments. Twelve accounts, and the two totals agree.

Fig 7.1Trial balance

Drag to turn · click to replayDr $100,500.00 · Cr $100,500.00

Northwind's unadjusted trial balance, read card by card into two drums. They total the same, so every entry was posted in balance — which proves the arithmetic, not that every entry is right.

What it proves, and what it does not

It proves	It does not prove
Every entry had equal debits and credits	That the entry went to the right account
Nothing was lost between journal and ledger	That anything was recorded at all
The columns were added correctly	That amounts are right — 4,800 on both sides ties perfectly
No one-sided entry was posted	That the period is right — an October invoice booked in September ties

Those blind spots have names, and it is worth knowing them because they are what review is for. An error of omission never entered the books. An error of commission hit the right type of account but the wrong one — a utilities bill in rent. An error of principle hit the wrong type — a van in repairs expense. A compensating error is two mistakes that cancel. An error of original entry got the amount wrong on both sides. A reversal of entries swapped the debit and the credit. All six tie.

A trial balance that ties is necessary and nowhere near sufficient. It rules out one class of error completely, and says nothing at all about the others.

When it does not tie

A difference is not a number to stare at — it has a shape, and the shape names the mistake. Learn these three and you will find most breaks in under a minute.

The difference	What it usually means	What to do
Divisible by 9	Two digits transposed — 8,400 typed as 4,800	Difference ÷ 9 gives the gap between the two swapped digits; look for figures that contain such a pair
Even, and half of it matches a posted amount	That amount was posted to the wrong side — it moved the gap by twice its size	Search for an amount equal to half the difference
Equal to a single posted amount	One side of an entry was left out, or a line was posted twice	Search for exactly that amount

Read the difference before you read the ledger.

Your turn

This trial balance does not tie

One figure was typed wrong on the way in. Do not hunt line by line — read the difference first, then look only at the accounts that could produce it.

This trial balance does not tie
Row	AAccount	BName	CType	DDebit	ECredit
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Total debits97,850.00

Total credits101,450.00

Difference(3,600.00)

Transposition — 3,600.00 ÷ 9 = 400.00 — two adjacent digits swapped, differing by 4.

Decimal slide — A figure of 400.00 entered as 4,000.00 (or the reverse) leaves exactly this gap.

Sign reversed — Half the difference is 1,800.00 — a figure of that size posted with the wrong sign explains it.

Check yourself

The $450 power accrual is debited to rent expense instead of utilities expense. Does the trial balance tie?

Where this lesson's rules come from

Requirements, conventions and mechanics are three different things. These are the sources behind the requirements — and the ones marked as conventions are ours, not the standard-setters'.

SEC Staff Accounting Bulletin No. 99 (1999)Materiality is not a percentageFree to read
ASC 250Accounting Changes and Error CorrectionsFree after registration

The full map is in US GAAP, and where these rules come from.

The words this lesson teaches

Each links to its definition in the glossary, where it also states the authority behind it and the components that render it.

In the founder glossary

The ideas in this lesson, explained for the founder who runs the company. Each has its own entry in the founder glossary.