My trial balance does not balance. How do I find the error without redoing everything?

Do not start again. The difference itself tells you what kind of error you are looking for, and checking it in the right order usually finds the problem in a couple of minutes rather than an hour.

Work out the difference, then test it

Take the gap between your two totals and run it through four checks, in this order. Each one is faster than the last resort of re-adding everything.

Is the difference divisible by 9? Then you have probably transposed digits: written 540 as 450, or 1,290 as 1,920. Transposition errors always produce a difference that is a multiple of 9, which is a genuinely useful fact and one almost nobody is taught. Scan for two digits swapped.

Is the difference exactly the amount of a transaction you recognise? Then the entry has gone in on one side only. Find it and post the other half.

Is the difference exactly double a figure you recognise? Then the entry is on the wrong side. A 300 debit posted as a 300 credit throws the balance out by 600, not 300. This one catches people constantly, because they look for 600 and the error is a 300.

Is it a round number like 100 or 1,000? Then suspect an addition error in a column rather than a posting error.

The errors a trial balance will never find

This is the part that carries marks in the written questions, and it is worth knowing cold. A trial balance only proves that debits equal credits. It does not prove the entries are right. Six kinds of error survive it:

• Omission — the transaction was never entered at all, either side.
• Commission — right amount, right side, wrong account of the same type (rent paid posted to insurance).
• Principle — right amount, wrong type of account, typically capital expenditure posted as revenue expenditure.
• Original entry — the wrong figure entered, correctly, on both sides.
• Reversal — debit and credit the right amounts but swapped between accounts.
• Compensating — two separate errors that happen to cancel out.

A question asking "will this error be revealed by the trial balance?" is testing exactly this list, and the answer for all six is no.

If it still will not balance

Open a suspense account for the difference so you can carry on, then clear it as you find each error. That is what the suspense account is for, and questions often start you at that point: here is a suspense balance, here are the errors, correct them and show the suspense account closing to nil.

Work through those corrections as journal entries with a narrative, not as mental arithmetic. The journal forces you to name both sides, and naming both sides is what stops you fixing one error by introducing another.