How to Calculate Your Quarterly VAT Without an Accountant

The modelo 303 (the quarterly VAT return) is the form you use to declare VAT every quarter. For many autónomos (self-employed workers) it’s the first tax obligation they face, and also the one that causes the most confusion at first. Not because it’s especially complex, but because nobody explains exactly what you need to fill it in or how the calculation works underneath.

The good news is that the calculation itself is simple. The tricky part, if there’s anything tricky at all, is having your data well organized before you sit down to fill it in.

This article adapts to your territory. The VAT rates (21%, 10%, 4%) and the way it’s calculated (output VAT minus input VAT) are the same throughout Spain, so the calculation and examples work wherever you pay tax. The only thing that changes in Navarre or the Basque Country is the form and the deadlines: pick yours in the “Where do you pay tax?” selector in the deadlines section.

What exactly is the VAT you declare

The VAT (IVA) you pay to the Spanish Tax Agency (Agencia Tributaria) each quarter is not a tax on your income. It’s the difference between the VAT you’ve charged your clients and the VAT you yourself have paid your suppliers.

When you issue an invoice with 21% VAT, that percentage isn’t yours. You’re an intermediary: you collect it on behalf of the State and pay it over to the Agencia Tributaria each quarter. This VAT is called output VAT (IVA repercutido).

On the other hand, when you pay a supplier’s invoice that includes VAT, the VAT you’ve paid is deductible. That’s called input VAT (IVA soportado). If you want to dig deeper into the difference, here we explain in detail what input and output VAT are.

The amount to pay is simply: output VAT − input VAT.

If the result is positive, you pay that difference. If it’s negative (you’ve paid more VAT than you’ve collected), you can offset it in the following quarters, or request a refund at the end of the year. If you want to do a quick calculation with your own numbers, try our free quarterly VAT calculator.

The data you need before you start

To fill in the modelo 303 you need three things:

1. The total of the invoices you’ve issued, grouped by VAT rate. If they all carry 21%, that’s a single number. If you have operations at 10% or 4%, you need them separated. These are the VAT rates in force in 2026.

2. The total of your deductible expense invoices, also grouped by VAT rate. Only expenses directly related to the activity, and which have a complete invoice with your details, count here.

3. Special operations, if any: intra-Community operations, exports, operations with reverse charge (inversión del sujeto pasivo). If your activity is straightforward and you only invoice Spanish clients, you probably don’t have any.

If you keep your income book and expenses book up to date, you have everything you need. The modelo 303 is basically a summary of those two books.

The calculation step by step

Let’s take a concrete example. An autónomo who, in the first quarter, has issued invoices for 10,000 euros of taxable base at 21%, and has had deductible expenses of 2,000 euros of taxable base at 21%.

• Output VAT: 10,000 × 21% = 2,100 euros.
• Input VAT: 2,000 × 21% = 420 euros.
• Amount to pay: 2,100 − 420 = 1,680 euros.

Those 1,680 euros are what gets paid to the Agencia Tributaria before 20 April.

If in that same quarter they’d also had expenses at 10% (a renovation, say), they would calculate the input VAT of that invoice separately and add it to the total input VAT. The procedure is the same, just with more rows.

The modelo 303 boxes that matter most

The modelo 303 has many boxes (casillas), but for an autónomo with a simple activity, the ones you’ll actually fill in are few (these are the boxes of the modelo 303, used in the common territory and the Basque Country; in Navarre, the modelo F-69 has its own numbering, though the VAT rates and the logic are identical):

• Box 01: taxable base of operations at the general rate (21%).
• Box 03: accrued VAT at 21% (the result of box 01 × 0.21).
• Box 28: taxable base of deductible input VAT.
• Box 29: amount of deductible input VAT.
• Box 46: result of the settlement (output VAT − input VAT). This is the amount to pay or to offset.

If you have operations at 10% or 4%, you’ll also use boxes 04/06 and 07/09 respectively.

The rest of the boxes are designed for specific situations: recargo de equivalencia (the equivalence surcharge regime), intra-Community operations, intra-Community supplies, etc. If you don’t know what a box is for, you probably don’t need it.

The deadlines

The form you file and its dates depend on where you pay tax:

If the last day falls on a holiday or weekend, the deadline extends to the next working day. And a territorial detail: in the Basque Country and Navarre, your VAT is handled by your regional (foral) tax authority when your tax domicile is there and your turnover doesn’t exceed €10 million a year (the case for almost all self-employed workers); above that threshold, it’s shared with the State.

When it makes sense to do it without an accountant

It depends on the complexity of your activity. If you only invoice Spanish clients, at the general rate of 21%, with no intra-Community operations or special situations, the modelo 303 is perfectly manageable without an accountant.

What you do need in that case is to have your data in order: the income and expenses books up to date, the invoices stored with their complete tax details, and a bit of time to check that the totals add up before filing.

If you have clients in other EU countries, if you apply reduced VAT rates, if you have employees, or if your activity mixes taxable and exempt operations, the complexity rises enough that an accountant is worth what they charge.

The dividing line isn’t whether you’re capable of understanding it, but whether the time you invest in learning it and doing it yourself is worth more or less than what an accountant charges. That’s a decision that depends on each person.

The mistake that costs the most

The most common mistake isn’t getting the calculation wrong. It’s not having your expense invoices in order and leaving input VAT undeducted because you can’t find the corresponding invoice.

Every professional expense invoice you don’t include in the modelo 303 is VAT that the Agencia Tributaria doesn’t give back to you. Over the course of the year, those amounts can be significant.

The solution is simple but requires discipline: keep every expense invoice the moment it’s received, record it in the expenses book, and don’t leave that task for the end of the quarter.

How does Cuéntamo help with this?

The step-by-step calculation we’ve gone through is exactly what Cuéntamo’s freelance module does for you. From the transactions you record, with their VAT rate, it separates the output VAT from your issued invoices from the input VAT on your expenses, and gives you the difference quarter by quarter, broken down by VAT rate so it lines up with the modelo 303 boxes.

Precisely because “the mistake that costs the most” is leaving input VAT undeducted, keeping the expenses book current stops being an end-of-quarter scramble: you record each invoice when it arrives and it already counts. And if a quarter comes out in your favor, Cuéntamo carries that VAT to offset forward into the following quarters so none of it is lost.

To avoid entering invoice by invoice, you can import your bank statement and reconcile the transactions against your records: that way the quarter’s calculation is built on real data, not on what you remember at the last minute. If you want a quick calculation with your own figures before recording anything, there’s the quarterly VAT calculator; and if you want to fully understand both sides of the operation, the article on input and output VAT.

The freelance module is part of Cuéntamo Más. You can get started at cuentamo.com.

Frequently asked questions

How is the quarterly VAT to pay calculated?

The VAT to pay is the difference between output VAT (the one you’ve charged your clients) and input VAT (the one you’ve paid your suppliers on business expenses). It isn’t a tax on your income, but on that difference.

What do I need to fill in the modelo 303?

Three things: the total of the invoices you’ve issued grouped by VAT rate, the total of your deductible expense invoices also by VAT rate, and any special operations. With your income book and expenses book up to date, you have everything.

What if my quarterly VAT result is negative?

If you’ve paid more VAT than you’ve collected, the result is negative and you have a balance in your favour: you can offset it in the following quarters or request a refund at the end of the year.

Does it make sense to file the modelo 303 without an accountant?

If you only invoice Spanish clients at the general rate, with no intra-Community operations or special situations, it’s perfectly manageable on your own. If you have clients in other EU countries, apply reduced rates, or your activity is more complex, an accountant is usually worth it.

What are the deadlines for filing the modelo 303?

In the common territory, the first three quarters are filed from the 1st to the 20th of the month following the close (April, July, and October) and the fourth runs until 30 January (not the 20th: a common confusion). In the Basque Country the deadline is the 25th and the fourth quarter goes in the annual summary (modelo 390) from 1 to 31 January; in Navarre you use the modelo F-69 with the first-20-days deadline. You have the detail by territory above.

Figures for 2026. The general (21%) and reduced (10%) VAT rates have been in force since 2012 (RDL 20/2012); the super-reduced rate (4%), since 1995 (Law 37/1992 on VAT). The foral deadlines and forms come from the regional tax authorities of Navarre, Bizkaia, Gipuzkoa and Álava.

This article is checked against official sources and reviewed periodically. If you spot anything out of date, email us at [email protected].