How fiscaldoo calculates deductible VAT

What is it for?

On a supplier invoice, VAT is only deductible to the extent the law allows. fiscaldoo decides that part line by line, by the Expense category, the Account or the product's category, and writes it in the Deductible column. What is not deductible stays in the expense; what is deductible goes to the period's deductible VAT.

Pending validation by a certified accountant: percentages and VAT Code (CIVA) articles cited (art. 21(1)(b), and the exceptions to the exclusion); the product holds them as data that can change, not as validated law.

When to use it?

• Purchases of fuel, electricity for vehicles and other expenses on which VAT is only partly deductible.
• You want to know why a line of a supplier invoice shows Deductible at 50 % and not 100 %.
• The percentage for an expense has changed (new law) and you need to close the old rule and open a new one.

If the company only deducts part of the VAT on all purchases because it carries out operations with and without the right to deduct, that is a different matter: see pro rata.

Where to find it?

• Use: Accounting › Record › Supplier invoices, in the Expense category column of each line, with the Accountant or Fiscal officer profile.
• Configure the rules: Accounting › Declare › VAT › What is there to do with the VAT?, in the VAT configuration group (VAT deduction rules and Expense categories). The Certified Accountant / Fiscal Manager profile with Fiscal officer sees this group; the Accountant only sees VAT configuration and Form 30 classification, without the rules. The administrator gets there through the Settings, in the VAT (PT): rules and tables block.
• You can also find them by typing “regras de dedução” in the menu search.

Before you start

• To view or change the rules: Fiscal officer profile (with Certified Accountant / Fiscal Manager).
• To post the invoice and check the result: Accountant profile. See the supplier invoice article.
• The rules are per company: check the active company in the top right corner.

How to use it

1. Open VAT deduction rules. The list shows, for each rule, the Account, the Product category, the Expense category, the VAT deductible (%), the Legal reference, Valid from and Valid until. In the demo there are seven rules, all by expense category: diesel, LPG, natural gas and biofuels at 50.00 %; petrol at 0.00 %; vehicles with full deduction and electricity for electric and plug-in hybrid vehicles at 100.00 %.
2. Each rule has one target: an Expense category, an Account or a Product category. When more than one rule fits the same line, the Expense category rule wins, then the Account rule, then the product's category rule (the closest one in the tree). With no rule, the line stays at 100 %.
3. On a supplier invoice, open a line and choose the Expense category, for example Fuel: diesel. The Expense category window opens with “The account 6228 Outros was replaced by 6242 Combustíveis, the account of the category "Fuel: diesel".”; click Close.
4. Enter the Price (100,00) and the 23% tax. The line shows Deductible 50 % and Deductible VAT €11.50.
5. Confirm the invoice. The rule's percentage stays on the line; changing the rule later does not change lines already posted.

Expected result

For €100.00 + €23.00 of VAT on diesel (FTF/2026/00048, total €123.00), the ledger shows:

Account	Debit	Credit
6242 Combustíveis (expense)	€100.00
6242 Combustíveis (splits the expense)		€50.00
6242 Combustíveis (“base of the expense (VAT partly deductible)”)	€50.00
6242 Combustíveis (“non-deductible VAT (CIVA art. 21.º)”)	€11.50
2432 IVA - Dedutível	€11.50
2211 Fornecedores gerais		€123.00

The expense ends up at €111.50 (€100.00 plus the €11.50 of VAT that is not deducted) and the period's deductible VAT goes up by €11.50. The non-deductible VAT line cites art. 21, which applies in this example; with pro rata it cites art. 23.

Important notes

Changing a percentage: close the rule and open another

A rule has Valid from and Valid until. The rule applied is the one in force on the invoice date. To change the percentage, fill in Valid until on the old rule and create another, with the new percentage and Valid from. Two rules for the same target with overlapping dates are refused (see “Common problems”).

A rule “in use” is not protected: do not rely on it

The product says that a rule used on posted lines cannot be changed or deleted, but that did not hold in the demo: after posting two diesel invoices, the diesel rule was changed from 50 % to 60 %, closed before the invoice dates and deleted, without being refused. The posted invoices did not change. Do not change or delete rules already used: close them with Valid until and create the new one.

Percentage entered by hand

You can change Deductible on the line. The change is recorded with the reason “Manual override of the CIVA art. 21 default rule”.

What the screen does not decide

fiscaldoo does not check whether the expense is deductible by law: it applies the rule that is there. Categories without a rule (for example Electricity or Water) stay at 100 % and the product warns you. Pending validation by a certified accountant: which categories without a rule should have a percentage, and art. 21(2).

Common problems

“The validity of this rule overlaps rule …”

• Symptom: when saving a new diesel rule from 01/06/2026: “The validity of this rule overlaps rule "Combustível: gasóleo — 50.0 %" for the same target — close the old rule (valid to) before creating the new one.”
• What to do: fill in Valid until on the old rule, on a day before the new rule's Valid from, and save the new one.

“Fill in either the account, the product category or the expense category …”

• Symptom: “Fill in either the account, the product category or the expense category — exactly one of the three, never more, never none.”
• What to do: leave only one of the three targets filled in.

Percentage above 100 or end before start

• Symptom: “The deductible percentage must be between 0 and 100.” and “The validity end date cannot be earlier than the start date.” The message appears in English.
• What to do: use a value between 0 and 100 and a Valid until on or after the Valid from.