Common Mistakes in Quarterly Tax Returns and How to Avoid Them

1. Filing the return after the deadline

One of the most common mistakes is forgetting the deadlines for filing the quarterly tax return. The Tax Agency sets very specific deadlines that must be met each quarter:

• 1st quarter (January – March): by April 20

• 2nd quarter (April – June): by July 20

• 3rd quarter (July – September): by October 20

• 4th quarter (October – December): by January 30 of the following year

If filed after the deadline, the Tax Agency may apply surcharges ranging from 1% to 20%, depending on how much time has elapsed.

✅ How to avoid it: use an up-to-date tax calendar and set reminders in your diary or accounting software.

2. Not reconciling input VAT and output VAT

Another frequent mistake in the quarterly VAT return is not having purchase and sales invoices properly recorded. Input VAT (what you pay on your expenses) must be offset against output VAT (what you charge your customers).

If invoices are not correctly accounted for, the settlement will be wrong and you will have discrepancies with the tax authorities.

✅ How to avoid it: reconcile your invoices every month, do not wait until the end of the quarter. Using invoicing software that automatically imports your expenses helps reduce errors.

3. Confusing tax forms

Depending on your activity, you will need to submit different forms alongside the quarterly tax return:

• Form 303: quarterly VAT

• Form 130: instalment payments of personal income tax (IRPF) for freelancers under direct assessment

• Form 131: for freelancers under the objective estimation method (módulos)

• Form 111: withholdings on employees and professionals

• Form 115: withholdings on rental income

Many taxpayers make the mistake of submitting only one form when they are actually required to submit several.

✅ How to avoid it: review your tax situation with your accountant or on the Tax Agency website before each quarter.

4. Including non-deductible expenses

In a rush to pay less tax, some freelancers include expenses that are not deductible in their quarterly return. For example: personal clothing, unjustified meals, or trips not related to professional activity.

The tax authorities tend to be very strict on this matter and, in the event of an inspection, may demand repayment of the deducted VAT plus penalties.

✅ How to avoid it: make sure all your expenses are directly related to your activity and that you keep the correct invoice (simple receipts are not sufficient).

5. Calculation errors and accounting discrepancies

Another common mistake is entering incorrectly totalled amounts or duplicate invoices. Although it may seem like a minor detail, it can produce a wrong result in your quarterly return.

✅ How to avoid it: keep organised accounting records and review the calculations before submitting the form. If you use Excel, double-check the figures; if you use an ERP or accounting software, rely on automation to minimise errors.

6. Not filing a return even when there is no activity

Many freelancers think that if they have had no income or expenses, they do not need to file the quarterly return. This is incorrect: in most cases, the obligation still exists even when there is no activity.

✅ How to avoid it: even if your quarter has been at "zero", submit the forms on time with a nil or no-activity result.

7. Not reviewing the data before submitting

It may seem obvious, but a transcription error in the tax ID number, the taxable bases, or the number of invoices can cause the tax authorities to reject the return or consider it incorrect.

✅ How to avoid it: take a few final minutes to review all the data before confirming the submission.

The quarterly tax return is an obligation that cannot be taken lightly. Filing it incorrectly or after the deadline can mean unnecessary surcharges and penalties. With organisation, the right tools and careful review, most errors can be easily avoided.

If you want to simplify your administrative tasks, the most advisable approach is to use management software or work with an advisory firm that supports you at each filing. This way you will gain peace of mind and avoid problems with the tax authorities.