From payment to the F24 and the withholding certificate

On 28 April 2026 a small agency in Turin pays a translator's invoice: a fee of 2,500 €, an INPS surcharge of 100 €, VAT at 22%, for a total of 3,172 €. It holds back 520 € and transfers the rest. Then nobody checks the calendar: 16 May falls on a Saturday, and the real deadline is Monday 18 May.

From the invoice to the net amount payable

The invoice of a professional outside the flat-rate scheme usually has three layers: the fee, any pension surcharges, and VAT worked out on the lot. The client pays the total less the withholding, and the gap between those two amounts is what it must later hand to the Treasury.

VAT does not appear among the amounts the Agenzia's page declares subject to withholding. The course calculator therefore keeps the two levies apart: withholding on the fee plus the INPS surcharge, VAT on the fee, the INPS surcharge and any professional fund contribution.

Back to the translator's invoice. The INPS surcharge is 4% of 2,500 €, so 100 €. The VAT base is 2,600 €, and VAT at 22% comes to 572 €. The invoice total is 3,172 €. The withholding base is 2,600 €, because VAT stays out, and the withholding at 20% comes to 520 €.

The net amount payable is the invoice total less the withholding: 3,172 − 520 = 2,652 €. That is the bank transfer. The 520 € does not stay with the agency: it is a debt to the Treasury that comes into being at the very moment of payment and must be cleared by the deadline.

Swap the INPS surcharge for a professional fund contribution and the sum changes in one place only. The contribution enters the VAT base but stays out of the withholding base. The calculator asks for the contribution rate as an input, since it depends on which fund the professional belongs to.

The two invoices share a total and differ in withholding. It is the quickest way to see that the kind of surcharge matters more than its size: one hundred euros of INPS surcharge enter the base, one hundred euros of fund contribution do not, and the twenty-euro gap shows up in the transfer.

The payment deadline

The page on how and when to pay sets the deadline plainly: withholding agents pay the tax withheld by the 16th of the month after the month of payment. The reference point is the month in which the fee was paid, not the month of the invoice nor that of the work.

A practical consequence follows. An invoice received in March and paid in April produces a withholding due by 16 May. A December invoice paid in January pushes the payment to 16 February of the next year. The withholding calendar follows the cash book, not the invoice register.

The same page provides for a shift: where the deadline falls on a Saturday or a public holiday, payment moves to the next working day. In 2026, 16 May is a Saturday, so withholding on fees paid in April is due by Monday 18 May.

Split payments and advances on a bill

Because withholding happens at the time of payment, a bill settled in instalments produces several withholdings, one per payment. Each instalment has its own base, worked out on the share paid, and its own deadline, set by the month in which that instalment left the account.

The same goes for an advance paid before the work is done. The page on income subject to withholding confirms it indirectly: when excluding fees below 25.82 euros, it adds that the exclusion does not cover advances on work worth more in total. An advance is therefore a fee in every respect.

For a small firm's cash planning the rule has a concrete effect. A bill paid off over three months produces three payments to the Treasury in three different months, and the payment log must record each one. Lumping them onto the last instalment would push back a debt that has already fallen due.

Form F24 and tax code 1040

Payment is made on form F24, quoting tax code 1040. The page adds a constraint on the channel: withholding agents holding a VAT number must pay electronically only. A company or sole trader with a VAT number cannot therefore hand in a paper F24 at a bank counter.

Code 1040 identifies withholding on self-employment income and separates it from every other tax paid on the same form. A wrong code does not make the payment vanish, but it books it against a different debt from the one created when the fee was paid.

Whatever the channel, keep the proof of payment next to the invoice and the log entry for the same fee. If the tax office comes asking, those three documents together show that the amount held back reached the Treasury on time.

The official F24 instructions are published by the Agenzia as PDF files. This course has not read them and does not reproduce them field by field. The linked form guide walks through filling in the payment step by step, relying only on the descriptive pages that can be read.

• Section of the form: Erario, the State Treasury
• Tax code: 1040, withholding on self-employment income
• Channel: electronic, compulsory for a withholding agent holding a VAT number
• Deadline: the 16th of the month after payment, shifted to the next working day where needed

The withholding certificate

Paying over settles things with the Treasury, not with the professional. The page on certifying withholdings states that the withholdings must be certified by whoever made them. The professional needs that certificate to set them against their own tax.

The certificate must state the total amount of sums and values paid, the withholdings made, the tax deductions applied and the social contributions. It may also carry optional data, such as the professional fund contribution or VAT.

• Required: total amount of sums and values paid
• Required: amount of the withholdings made
• Required: tax deductions applied and social contributions
• Optional: professional fund contribution, VAT and other non-mandatory data

The deadline and the model for the annual certificate are set in instructions the Agenzia publishes every year as PDF files. This course has not read them and puts no date on them. What always holds is consistency: the amounts certified must match those withheld and paid under code 1040.

On the professional's side

For a resident professional the 20% withholding is an advance on IRPEF. It is not a final cost: in the tax return the withholdings suffered during the year are subtracted from the tax owed on that income. That is what the Agenzia's page means by the words as an advance.

For a non-resident working in Italy things differ. The 30% withholding is a final tax and is not credited in an Italian return: it closes the levy on that fee. The client should therefore expect no later adjustment, in either direction.

For the client, though, paying over does not change. Whether the withholding is 20% as an advance or 30% as a final tax, the payment is still when it happens and the 16th of the next month is still the deadline. The rate and the fate of the money change, not the calendar.

The certificate is thus the document linking both sides. A missing or wrong certificate does not alter the duty the client has already met, but it deprives the professional of the paper that proves the withholdings suffered. That is the practical reason to prepare it with the same care as the payment.

A payment log so no deadline slips

The typical risk in a small business lies not in the arithmetic but in memory. Paying a bill is a one-off event, and the payment due the following month shows up on no bank statement. Without a reminder, the 16th goes by and nobody notices.

A simple log solves it: one row per fee paid, with payment date, professional, base, withholding and reference month. At the start of each month, add up the withholdings on the previous month's payments: that is the amount to pay under code 1040 by the 16th. The same log will serve for the certificate.

The log is not a duty imposed by the Agenzia's page: it is a working tool. Its merit is to bring together in one row the three moments the law keeps apart, namely payment, payment over and certification, and to make whatever is missing visible at a glance.