# Set Up Filing Periods

Filing periods have to match what you registered for with your tax authority, exactly.

Get them right once at the start and every return afterwards lines up on its own; get them wrong and every return needs manual arithmetic.

![The VAT Settings tab of Finance Settings, alongside Tax Rates, VAT Filing Settings and a greyed-out Construction Industry Scheme. A Registration section carries a VAT Registered toggle set on, a registration number label, the number GB418277364 and a registration date. A Filing section sets VAT Accounting Basis to Accrual (Standard) and Filing Frequency to Quarterly, noting that changing the basis recalculates draft returns while returns already filed are unaffected.](https://www.sorviai.com/help/tax-filing/vat-settings.png)

*Accounting basis and filing frequency are what decide which transactions land in which period.*

## Rates and treatments

Two settings decide the tax on any given line, and they work together. The rate is what percentage applies; the treatment is whether it applies at all.

- **Tax rate** (on the item or line): The percentage. Set as a default on the item and overridable per line.
- **Tax treatment** (on the customer or vendor): Whether tax is charged, and at which rate group. This is what makes an overseas sale zero-rated without anybody choosing it.

> **Tip:**
>
> **Wrong-looking tax is usually a treatment**
>
> A domestic sale that came out zero-rated is nearly always a customer whose treatment says overseas or exempt. Check the customer before you check the item.

## Changing periods later

| Change | When it is safe |
| --- | --- |
| Frequency, monthly to quarterly | From your next unfiled period, if the authority agreed. |
| Period start date | Only if no return has been filed on the old dates. |
| Accounting basis | At a period boundary, with the authority's agreement. |
| Adding a tax rate | Any time. Existing transactions keep their rate. |
| Editing a tax rate percentage | Never. Add a new rate instead. |

> **Warning:**
>
> **Never edit a rate percentage**
>
> It would silently restate the tax on every transaction that used it, including periods already filed. When a rate changes, create a new rate and switch items over to it.