Closing a month
A checklist confirms the month is actually done, then locking it stops the books from moving under you.
The close checklist
Before you lock a period, Nummio checks that every account is reconciled, the review queue is empty for that stretch of time, and there are no unposted drafts hanging around. The checklist reflects what actually has to be true for the month to be done — it isn't a formality you can skip past.
Locking a period
Locking a period is enforced where it matters — the posting engine itself rejects a new transaction dated into a locked period, not just a warning in the interface. Once a month is locked, its numbers don't move again without going through the unlock path.
Adjusting entries
Sometimes a correction has to land in a period that's already locked — a year-end adjustment from your accountant, for instance. External Accountants can post adjusting entries directly into a locked period; Owners and Bookkeepers can do the same through an explicit unlock. Either way, the entry is typed as adjusting and logged loudly, never quietly.
Why it's worth doing every month
A locked period is a report that won't change on you later. Closing monthly, instead of once a year, is what makes that promise mean something by tax time.