Where the amount to pay comes from
The amount to pay on modelo 303 is not one subtraction that ignores the regime. In the general case it is output VAT minus deductible input VAT. If the regime adds equivalence surcharge or other boxes, those figures enter too.
The subtraction, and what the regime adds
You start from the VAT on the invoices you issue. You subtract deductible VAT on expenses, when the invoice allows it and the expense belongs to the activity. If equivalence surcharge or another box of the regime applies, the result includes them. Reducing it to output minus input, and nothing else, leaves those cases out.
- Usual base: output minus deductible input.
- Regime boxes enter too, if they apply.
- The equivalence surcharge is not ignored.
The app starts from what you confirmed
Factura Fácil calculates the result from the invoices and expenses you confirmed. It can prepare the import file. It does not file modelo 303. If the regime is a special one, the boxes have to be that regime’s, not a slogan for the general case.
Common questions
Is the amount to pay always output minus input?
That is the usual subtraction. If the regime adds equivalence surcharge or other boxes, the result includes them too.
Does the app file the amount to pay?
No. It calculates it from confirmed invoices and expenses and can prepare the file. Submission is on the Tax Agency site.
Official sources
Informational text reviewed on 26 September 2026. It is not tax advice and does not replace the Spanish Tax Agency or your accountant. Deadlines, rates, and forms can change.