How to simulate the VAT return before closing the period

What is it for?

The VAT return simulation calculates the fields of the periodic return for any period, even halfway through it, without creating or touching any return. It shows you what the VAT amounts to before you generate the real return and, if needed, lets you correct the documents first.

The simulation always carries the mark “SIMULATION - not submitted, no fiscal value”. It creates no journal entries and communicates nothing to the AT: it is just a calculation, which you can repeat.

Pending validation by a certified accountant: how to read the return fields (the “field NN” numbering comes from the AT form), what each amount means in the return and whether the field layout the simulation uses (the 2027 form) is the right one for 2026 periods.

When to use it?

• You are halfway through the month or quarter and want to see the period's VAT so far.
• You are about to close the period and want to check the fields before generating the return.
• You want a file (XLSX or PDF) with the fields to show the certified accountant.

To prepare and submit the real return, see How to prepare and submit the periodic VAT return.

Where to find it?

Accounting › Declare › VAT › VAT return simulation, with developer mode on (without it, the item does not appear in the bar).

Before you start

• Certified Accountant / Fiscal Manager profile (or Administrator).
• The active company must be Portuguese and have its tax region set: otherwise the simulation is refused.
• Know the start and end of the period you want to simulate.

How to use it

1. Open Accounting › Declare › VAT › VAT return simulation. The window asks for the Period start and the Period end.
2. Type the two dates, for example 01/09/2026 and 30/09/2026, and click Simulate.
3. The window shows the mark “SIMULATION - not submitted, no fiscal value”, the Problems found (0 in this period) and the list Field, Type (Basis or Tax) and Value: 49 lines, 40 on the first page and 9 on the second. In September 2026, for example, field 1 has a basis of 219,00 and field 2 a tax of 13,14.
4. The Export to XLSX and Export to PDF buttons only appear after you click Simulate: before that the window only has Simulate. The XLSX has the simulation mark, the company (“Empresa Demonstração, Lda”), the period and one line per field (49, as on screen); the file name is simulacao_dp_iva_2026-09-01_2026-09-30.xlsx. The PDF, simulacao_dp_iva_2026-09-01_2026-09-30.pdf, has 3 pages, the mark “SIMULATION - not submitted, no fiscal value”, the title, the company, the start and end of the period and the Field, Type, Value table with the 49 fields (field 1: Basis 219,00; field 2: Tax 13,14; field 4: Tax 1.479,62; field 22: Tax 138,00), the same as on screen.
5. For another period, change the dates and click Simulate again: the list is replaced.

Pending validation by a certified accountant: how to read the fields cited.

Expected result

In a period that already has a return, the simulation amounts are those of the return. September 2026 has the return “2026/9 (v1)”, validated: the 13 simulation fields with an amount (1, 2, 3, 4, 22, 24, 61, 90, 91, 92, 93, 98 and 106) match those of the return to the cent (for example field 4, tax, €1,479.62). The other 36 fields are at 0,00 in both.

The simulation does not change the return, the lock dates or the journal entries. Each simulation is recorded in the fiscaldoo audit log, with the period, the number of fields and the problems.

Pending validation by a certified accountant: how to read the fields cited.

Important notes

“Problems found” only counts

The screen shows the number of problems (September 2026: 0; October: 1) but does not say which ones. To find out what is missing, open the return and read its checks, or the article How to prepare and submit the periodic VAT return. A 0 does not prove that the return is right either: it only says that the calculation found no problems.

A future period counts what is already posted

Since the simulation reads the existing journal entries, a period that has not ended yet only shows what has already been posted. December 2026, for example, already shows €441.60 in field 40, the amount of the pro-rata adjustment posted on 31/12/2026 (see Pro-rata), and 3 problems found.

Pending validation by a certified accountant: how to read the fields cited.

The simulation does not create the return

To generate and validate the return, use VAT return records; the simulation neither replaces nor creates it.

Common problems

“Choose a period whose end is not before its start”

• Symptom: Invalid Operation window when you click Simulate with the start 30/09/2026 and the end 01/09/2026: “Choose a period whose end is not before its start.”
• What to do: click Close, correct the dates and simulate again.

The export buttons do not appear or do nothing

• Cause: the export is of the simulation result shown in the window. Before Simulate the export buttons do not exist (the screen neither shows nor refuses them).
• What to do: click Simulate and then Export to XLSX or Export to PDF. Both files were opened and checked (49 fields).