Period locks and the trial balance sign-off

Why periods get locked

After you lodge a BAS, file a tax return, or send a year-end pack to your accountant, the numbers underpinning those reports must stop changing. If someone backdates a transaction into a closed period the next day, the lodged figures and the live ledger silently diverge, and you discover the problem only when the ATO sends a please-explain.

A period lock prevents that. Posting, editing or deleting any transaction with a date inside a locked period is rejected at the point of entry.

Locking a period

From Accounting, then Period Locks, then New lock:

1. Pick the lock date, typically the last day of the period you want to close (e.g. 30 September for the Q1 BAS)
2. Add an optional note ("Q1 24-25 BAS lodged")

From that moment on, every dated transaction must have a date strictly after the lock date. The lock applies to invoices, bills, expenses, manual journals, payments, and bank reconciliation lines.

Unlocking when you need to

Mistakes happen. If you genuinely need to fix a transaction inside a locked period, say, an invoice was issued to the wrong customer, open the period lock and click Unlock temporarily.

While unlocked, the lock note shows in amber across the top of every accounting page so the unlock is impossible to miss. Re-lock the period as soon as the fix is in. The unlock event itself is recorded in the audit log with the actor and reason.

Trial balance sign-off

A separate but related concept. The Trial Balance page has a Sign off action at the bottom. When you click it:

1. Every account's closing debit and credit balance at the as-at date is snapshotted to an immutable record
2. A PDF of the trial balance is generated, watermarked with the date and the signer
3. The signed snapshot appears in the Trial Balance Comparative report so future periods can compare against it

Signing off a trial balance does not lock the period, they are independent. Most practices sign off the year-end TB after the period is locked, and use the signed PDF as the formal handover artefact to the tax agent.

A sensible cadence

• Lock at quarter-end after lodging BAS
• Sign off the trial balance at year-end after final adjustments
• Lock 30 June once the year-end pack is finalised

For anything more frequent (e.g. monthly close), lock at month-end once you have reviewed the P&L and balance sheet and emailed the management pack.