Forgot income on your Modelo 130? How to file a complementaria, step by step

Nick · 2026-10-16 · Updated 2026-10-16 · Figures as per the rules in force on 2026-10-21

If you left income off your Modelo 130, you file a complementaria: the same quarterly form, marked supplementary, with all figures recalculated from scratch. Field [18] holds what you already paid; field [19] is the difference now due. Complementarias can only increase the amount owed — if the correction would reduce it, use a rectificativa instead (LGT art. 120.3). Filed before the voluntary deadline, there is no surcharge under LGT art. 27. In the real 3Q 2026 case in this article, the extra payment was 1,515.25 €.

What a complementaria actually is

A complementaria is not a correction slip. It is the full Modelo 130 for the same quarter, refiled from scratch with the correct numbers and marked as supplementary. Field [18] carries the amount you already paid; field [19] — the only new payment — is the difference between what you should have paid and what you actually paid.

Modelo 130 is the quarterly IRPF advance payment for autónomos under simplified direct assessment: 20% of year-to-date net income, minus anything already paid in earlier quarters (RIRPF art. 110.1 a)). When you leave income out of the original filing, the net income figure is too low, the 20% calculation is too low, and the payment is too low. The complementaria fixes all three.

One constraint matters from the start: a complementaria can only produce an amount to pay or leave the balance unchanged. If, after putting in the missing income, you discovered the total would actually go down — that cannot be a complementaria. That scenario calls for a rectificativa de autoliquidación under LGT art. 120.3, which is a separate process.

Why income was missing: the accrual rule

An autónomo who started activity on 1 July 2026 filed the Q3 2026 Modelo 130 on 13 October. The next day, two gaps emerged.

Work done in July–September, invoiced on 14 October. The service was delivered during Q3. In IRPF, income is assigned to the period in which it accrues — when the work is done — not when the invoice is raised or when payment arrives (LIRPF art. 14.1, the general accrual principle). The invoice date of 14 October does not move that income into Q4. It belongs in Q3.

This catches many expat autónomos off guard. If you are billing a client in the UK, the US, or anywhere else outside Spain, and the work crossed a quarter boundary, the income accrues in the quarter the work was done. Invoicing late does not delay the tax obligation.

Invoices to non-EU clients that were never entered. These had simply not been added to the income records before the filing.

The original return declared 7,713.00 € of income. The correct figure was 15,289.24 € — nearly double.

The complementaria, field by field

In the AEAT Sede Electrónica, open the Modelo 130 for Q3 2026, select «Declaración complementaria» as the type, and enter the número de justificante from your original filing. Field [18] takes what you already paid with the earlier return for the same quarter: 1,314.99 €. You enter all the figures for the full quarter — income, expenses, the works — as if filling the form for the first time.

The arithmetic: 20% × 14,651.19 € = 2,930.24 €; minus the 100 € minoración; [17] = 2,830.24 €. Subtract [18] = 1,314.99 € already paid: [19] = 1,515.25 €. The first payment is not refunded and not recalculated. You pay the gap.

The deadline and what it costs

The voluntary filing window for Q3 2026 runs until 20 October 2026. The complementaria was filed on 14 October — inside that window.

LGT art. 27 surcharges apply only when a declaration arrives after the voluntary period, without a prior request from AEAT. Inside the window, a complementaria is treated exactly like any other timely filing: the 1,515.25 € was paid by ordinary bank transfer, no surcharge, no penalty, no open case. Six days remained before the deadline; both filings were complete.

Had the complementaria gone in on 15 November instead, less than one full month after the 20 October deadline, the surcharge would have been the base 1%. On 10 December, with one full month of delay behind it, 2%. Each further full month adds 1%, and after twelve months it becomes 15% plus late interest. The mechanism is the same for all autónomos; the numbers just depend on how late.

Why the minoración did not change

Field [13] applies the reduction under RIRPF art. 110.3 c): a flat deduction per quarter for autónomos whose net business income in the previous year fell below certain thresholds. The thresholds used by AYFI:

The decisive number is last year's net income — not the [03] figure on the current form. This autónomo began activity on 1 July 2026, so their 2025 net income was zero, which is below 9,000 €. The minoración is 100 € per quarter.

The complementaria pushed Q3 2026 net income to 14,651.19 € — well above 9,000 €. But that figure is this year, not last year. The minoración rule looks backward, so 100 € stays in [13] on both the original filing and the complementaria.

This is a common source of confusion: the minoración depends on the previous year's net income regardless of how much you earn in the current quarter.

What this looks like if you're used to self-assessment or quarterly estimates

The mechanism is different enough from UK and US practice that it trips up autónomos who arrived in Spain after years of filing elsewhere.

UK self-assessment. As a sole trader in the UK, you keep records through the tax year (6 April to 5 April) and file one Self Assessment return — the SA100 with supplementary pages — after the year ends. Making Tax Digital for Income Tax (from April 2026, for qualifying income over £50,000) adds quarterly updates of income and expenses, but they carry no payment: the tax is still settled through the annual return and the January and July payments on account. If you make a mistake on your SA100, you can amend it online through your HMRC account, and HMRC calls it an amendment, not a "complementaria." The concept of filing the full period again, with a separate field for the amount already paid, does not have a direct parallel.

US estimated taxes (Form 1040-ES). The US quarterly payment is an estimate, not an accounting. You pay based on either the prior year's tax liability or a projection of the current year; you do not attach a schedule of actual income and expenses each quarter. Corrections flow through the annual Form 1040 (or adjusted quarterly payments), not through a separate supplementary form that re-runs the period from scratch.

Spain's approach is different on two points. First, Modelo 130 uses actual year-to-date figures every quarter — real income, real expenses, not estimates. Second, because the form is cumulative (it restates totals from 1 January every time), a forgotten invoice in Q3 does not stay isolated in Q3. It sits in the running total that Q4 will restate. Skip the complementaria and Q4 still catches up: [01] includes the forgotten income and [05] deducts the smaller amount paid, so the shortfall is paid in Q4. But it is paid late. The Q3 payment was understated, and the AEAT can claim a surcharge and interest on it, or a penalty if it finds the gap before you do. The annual Renta is a separate return and comes out right as long as the income is declared there. What the complementaria buys is paying the Q3 amount in its own quarter, inside the deadline, with no surcharge.

One practical note for anyone billing clients outside Spain: the AEAT Sede Electrónica is entirely in Spanish, and browser auto-translation renames the buttons in ways that do not match any written guide. Turn translation off for agenciatributaria.gob.es before you start. You will need your digital certificate or Cl@ve to file; a passport number alone is not enough.

AYFI prepares the fields for both the original filing and the complementaria — [01] through [19] — using the income and expense records you have entered. The filing itself is yours to submit in the Sede.

Frequently asked questions

Can I file a complementaria that results in a refund?

No. A complementaria can only result in an amount to pay or a smaller refund (LGT art. 122.2). If your correction would reduce what you owe, the mechanism is a rectificativa de autoliquidación (LGT art. 120.3), which follows a different procedure and can lead to a refund.

What surcharge applies if I file the complementaria after the voluntary deadline?

LGT art. 27 sets the surcharges: within twelve months of the deadline, 1% plus another 1% for each full month of delay, so even a filing a few days late costs 1%; after twelve months, 15% plus late interest from month thirteen. None of these apply when the complementaria reaches AEAT before the voluntary window closes.

Does the complementaria affect my Q4 Modelo 130?

Yes. Modelo 130 is cumulative: Q4 field [01] restates income from 1 January to 31 December, and field [05] deducts everything paid in the first three quarters. AYFI records the figures as actually filed, so the Q4 calculation picks up the complementaria automatically without any manual adjustment.

My Modelo 303 for the same quarter had not been filed yet — do I need a complementaria for IVA too?

No. If the 303 for that quarter was still open when you discovered the missing income, the new invoices go straight into that 303 as a normal first filing. No IVA complementaria is needed.

Sources

• RIRPF art. 110 — Instalment payment. Modelo 130
• LGT art. 27 — Surcharges for late declaration without prior request
• LIRPF art. 14 — Temporal attribution of income: accrual principle
• LGT art. 122 — Supplementary self-assessments