# Close a Period

Closing a period locks it against new and backdated transactions.

It is the only thing that stops a filed return quietly drifting away from the numbers you declared, and it costs nothing to do.

![The VAT Filing screen with its two tabs, Unsubmitted Return and All Returns, above a draft return marked Draft for the quarter to 30 September 2026.](https://www.sorviai.com/help/tax-filing/vat-return.png)

*A return stays a draft, and keeps recalculating, until somebody finalises it.*

## What closing does

| Action | In a locked period |
| --- | --- |
| Saving a new invoice or bill dated in it | Refused |
| Editing a transaction dated in it | Refused |
| Posting a journal dated in it | Refused |
| Running a report for it | Allowed. Reports never change data |
| Recording a payment dated after it | Allowed, even against an invoice inside it |

> **Note:**
>
> **It locks by date, not by document**
>
> A period is Open or Locked, and the lock is applied to anything whose accounting date falls inside it. Nothing dated after the period is affected, including a payment settling an invoice from inside it.

## Unlocking

A locked period can be unlocked, and doing so is a decision rather than a convenience. Everything reported from that period, including a filed return, was based on numbers that can now change.

Unlocking is recorded. The product keeps who unlocked the period, when, and the reason they gave, so this is a step with your name on it rather than a quiet toggle.

- **Be sure the change is necessary**

  Most late items are better dated into the current open period, if your authority allows it.
- **Unlock, make the change, lock again**

  Give a real reason when you unlock; it is kept. Do not leave a period open while you think about it.
- **Re-run the return**

  Compare it with what you filed. The difference is what you may need to declare.
- **Note what changed and why**

  On the transaction, and somewhere your accountant will find it.

> **Warning:**
>
> **Unlocking changes filed numbers**
>
> Not hypothetically. A backdated bill in an unlocked period changes the input tax for a return you have already submitted. If that return went to HMRC, the figures they hold and the figures you hold have just diverged, and nothing reconciles them except you.