I cannot change a VAT rate or a deductibility rule already used

Symptom

You change the percentage of a tax or of a VAT deduction rule and, when you save, an Invalid Operation window opens. The change is not saved.

Message

When you change the percentage of a tax, in Accounting › Configure › General › Taxes:

“Tax "23%" is used on posted documents — its rate cannot be changed (it would corrupt the fiscal history of documents already issued). Use "Supersede rate" to create a successor tax instead.”

When you change a deduction rule already used:

“The deductibility rule "6221 Trabalhos especializados — 75 %" is used in posted purchase lines and cannot be changed (VAT deductible (%)). What happened: changing it would rewrite the VAT already deducted in those documents. How to fix it: close the rule (field "Valid to") and create a new rule with its own validity.”

When you delete the rule:

“The deductibility rule "6221 Trabalhos especializados — 75 %" is used in posted purchase lines and cannot be deleted. What happened: the rule is the evidence of the percentage deducted in those documents. How to fix it: close the rule (field "Valid to") and create a new rule with its own validity.”

When you close the rule on a date before the last document:

“The rule "6221 Trabalhos especializados — 75 %" can only be closed on or after the date of its last posted line (06/11/2026).”

Archiving a used rule (⋮ menu next to the name, Archive, and Archive in the Confirmation window) is also refused, with the rule's first message and (Active) in brackets. All of them were triggered in the demo database, with a user who only has the Certified accountant profile.

Verified causes

• The rate is already on posted documents. Changing the percentage would alter the fiscal history of those documents.
• The rule has already been applied to posted purchase lines. It is the rule that proves the percentage deducted.
• The end date is before the last document. The rule must cover every document that used it.

What to check

1. Whether the law really changed from a given date, or whether the wrong rate was chosen on a document. In the second case, the correction is made on the document, not on the rate.
2. The date from which the new rate or rule applies, and the legal reference. Pending validation by a certified accountant: the percentage and date of each new rate or rule.
3. The profile: these changes are made with the Certified accountant profile. With the Accountant profile, Configure has no Taxes, the VAT panel has no VAT deduction rules, and the tax, opened from a link, is read-only, without Supersede rate….

How to fix it

Supersede a VAT rate

1. Open the tax in Accounting › Configure › General › Taxes and the Portugal tab.
2. Click Supersede rate…. Supersede VAT rate opens, with the Current tax.
3. Fill in New rate (%), Valid from and Legal reference. Source URL (DRE) is optional.
4. Click Confirm.

The screen opens the new rate. In the demo, the 23 % purchase rate, superseded by 24 % from 01/01/2027, gave the tax “24% (a partir de 01/01/2027)”, with 24 % in Percentage.

Close a deduction rule

1. In Accounting › Declare › What is there to do with the VAT?, open VAT deduction rules and the rule.
2. In Valid until, type a date equal to or later than the last posted line, and save. In the demo, 30/11/2026 was accepted for a last line dated 06/11/2026.
3. Create the new rule with New, with the same account, its own Valid from, the VAT deductible (%) and the Legal reference. In the demo, the new rule for 6221, at 50 % from 01/12/2026, was accepted alongside the old one, closed on 30/11/2026.

More about the rules in How fiscaldoo calculates deductible VAT. While the old rule is in force, it keeps applying to invoices dated up to Valid until.

Who does it: Certified accountant.

Expected result

Posted documents stay as they were. New documents use the rate or rule in force on their date.

When to contact support

• The rate is refused without ever having been used.
• The Portugal tab of a Portuguese VAT rate has no Supersede rate… with the Certified accountant profile. With the Accountant profile, the button does not appear.

Information to send

• The name of the tax or rule and the company.
• The full text of the message, copied from the screen.
• The intended percentage, the date and the legal reference.