Who acts as a withholding agent, and how the single certificate (CU) is issued

On 12 March 2026 the owner of a small design studio in Bologna, a limited company with three employees, receives a certified email from a photographer. In 2025 the studio paid him 4,000 € in fees and withheld 800 € of tax. He wants his single certificate, the CU. Nobody in the office knows whether the deadline is 16 March or 30 April. The answer is both, for two different documents.

What a withholding agent does

The Revenue Agency's guidance pages do not define the withholding agent in the abstract; they describe what it does. Whoever pays employment income, or fees for self-employed work, keeps back part of the recipient's personal income tax (IRPEF) at the moment of payment, as an advance on that tax.

In practice the business stands in for the taxpayer for a slice of the tax. The employee or the professional receives an already reduced amount. The part held back never belongs to the business: it sits on its account for a few weeks and must then reach the Treasury through a payment made in the agent's own name.

Four duties follow from that description, and they come back every year. This course takes them in the order in which they show up in a small business's diary: withhold when paying, pay over by the monthly deadline, certify to the recipient, report to the Agency.

• Withhold: the obligation arises when money is paid, not when a contract is signed or an invoice arrives
• Pay over: amounts withheld go to the Treasury on form F24 by the 16th of the month after the payment
• Certify: early in the following year every recipient receives a single certificate, the CU
• Report: withholdings are declared to the Agency on form 770, or through the simplified route when its conditions are met

When a small business becomes an agent

Size is irrelevant. A limited company that hires its first employee becomes an agent with the first payslip it pays. A sole trader under the ordinary regime who settles an accountant's, a lawyer's or a translator's bill becomes one on the day of the transfer, even with no staff at all.

The page on employment income says so of employers paying wages and similar income; the page on self-employment repeats it for anyone paying a professional's fees. In both cases the trigger is a precise fact, the payment, rather than an intention or an accounting document.

The employment page also reminds readers that income treated like wages is broader than it looks: it covers, for example, pay to members of worker cooperatives and periodic allowances to a spouse. In a small firm, though, the typical cases remain ordinary salaries alongside professionals' invoices.

One exception matters a great deal for small businesses: the flat-rate regime, the forfettario. According to the Agency's page on its simplifications, a flat-rate taxpayer does not withhold tax at source, except on employment income and income treated like it. A flat-rate designer paying a consultant therefore keeps nothing back.

That does not take the flat-rate taxpayer entirely out of the picture. In their own income tax return they must list the tax codes of the people they paid without withholding, and the amounts. And once they hire an employee, they become a withholding agent on that salary exactly like any other employer.

Then there is the mirror case: a flat-rate professional on the receiving end. Their fees are not subject to the advance withholding, and they must give the client a statement confirming the income falls under the substitute tax. For electronic invoices the Agency provides a dedicated wording stating that the transaction is not subject to withholding.

How the base of the withholding is built, what happens to the social security surcharge on the invoice and how much reaches the professional's account are covered by a dedicated course and by the withholding calculator. This module is about what comes after the transfer: what the agent must do, over the year, with the money it held back.

The single certificate: what it attests

For the 2025 tax year, agents use the Certificazione unica 2026, the CU. The Agency brings into it employment and similar income, self-employment income, commissions, miscellaneous income and the rents from short-term lets. The form carries the year in which it is filed, not the year in which the money was paid.

The Agency's page on certifying withholdings sets a minimum content: the total of the sums and values paid, then the tax withheld, the tax credits applied and the social security contributions. Further data, such as a professional pension fund contribution or VAT, may be added but are optional.

What gets certified, then, is the gross amount paid and the part held back, not the net sum that landed in the recipient's account. That is the classic mistake of anyone rebuilding the CU from a bank statement: the transfer only shows what left, while the certificate must reconstruct the whole amount and the tax.

For the recipient the CU is no formality. A resident professional deducts the tax withheld from the IRPEF due in their own return and needs a document proving it. An employee finds in the CU the basis of their pre-filled return. A wrong certificate moves the error into somebody else's tax return.

Short version to the recipient, full version to the Agency

The CU comes in two versions with two addressees. The short version, the modello sintetico, is handed to the person who received the money. The full version, the modello ordinario, is sent to the Revenue Agency, electronically only. They describe the same payments, and neither replaces the other.

The form, its instructions, the filling-in software and the checking tool are published every year by the Agency in its CU section. The instructions are a PDF that this course has not read, so it does not reproduce them line by line. The linked form guide walks through the filing using the descriptive pages that can be read.

The 2026 CU deadlines

The general rule sets one date for both duties. The short version must reach the recipient by 16 March 2026 and, by the same date, the full version must be sent to the Agency. The exceptions on the Agency's page concern only the transmission to the Agency, never the delivery to the recipient.

First exception: when a certificate contains nothing but fees for self-employed work carried on habitually as a profession, or regular commissions from agency, brokerage, sales representation or business introduction, its transmission to the Agency may wait until 30 April 2026.

Second exception: a certificate made up solely of exempt income, or of income that is not declared through the pre-filled return, may be sent by the deadline of the agents' annual return. That deadline is 31 October, a Saturday in 2026, so the Agency's page gives 2 November 2026.

The word that decides is "exclusively". The exception is assessed one certificate at a time: the CU of a lawyer who received nothing but professional fees may go to the Agency by 30 April, while the CUs of the same office's employees follow the 16 March rule.

Watch the word "habitually" too. Someone who did a single one-off job for you does not practise a profession on a regular basis: their certificate falls outside the first exception and must be sent by 16 March, like the employees' ones.

From the CU to form 770

The CU does not close the agent's tax year. Form 770/2026, covering the 2025 tax year, is how agents report electronically to the Agency the tax withheld on employment and similar income, on self-employed fees, commissions and miscellaneous income, as well as on other categories that are rare in a small business.

The Agency's 770 page ties the two steps together explicitly: the 770 can be filed only if the agent has already sent its single certificates within the prescribed deadlines, which the same page lists as 16 March, 30 April and 31 October 2026. A certificate forgotten in March therefore blocks the autumn return as well.

Very small employers have a lighter route. From the 2025 tax year, an agent that pays only employment, self-employment or similar income, and that had no more than five employees on 31 December of the previous year, may join a simplified data reporting system that counts as filing the 770.

How the simplified system works is set by measures of the Agency's Director that this course has not read. The five-employee threshold is one condition, alongside the kind of income paid; before dropping the 770 it is wise to confirm with your tax intermediary that the route genuinely applies to you.

One point of method remains. The CU and the 770 tell the story of the same payments from two sides, and the F24 payments made during the year are the third. If the three sets do not match, the error already exists: it is better found in February, while preparing the certificates, than in October.