€6,000 of side work leaves €2,630 and a €2,090 bill in June

A designer with a job takes on three evening projects during 2026 and invoices €6,000 for them, with no partita IVA. Each client keeps 20% back and sends a certificate. Their salary is €35,000 of taxable employment income. Between the tax those fees add to their year and their share of the contribution, the work costs €3,369.60 — the clients withheld €1,200.00, and the remaining €2,089.60 falls due when the return for 2026 is filed.312

What is left of the €6,000 is €2,630.40.

The 20% is an instalment

Work done without a partita IVA is not untaxed and it is not taxed separately. It is a reddito diverso — an “other income” — under article 67, comma 1, lettera l) of the income tax code, which covers “i redditi derivanti da attività di lavoro autonomo non esercitate abitualmente”: income from self-employed work not carried on habitually. Article 71, comma 2 says what is taxable — the amount received in the year less the expenses specifically incurred to earn it. It then joins the rest of the person’s income and is taxed with it.12

The withholding is a payment on account of that. Article 25 of the 1973 assessment decree requires the client to withhold on payment “a titolo di acconto dell’imposta sul reddito delle persone fisiche dovuta dai percipienti” — on account of the income tax owed by the person receiving the money. The consolidated article still prints 15%, because the three provisions that raised the rate operated from outside it and are recorded as amendment notes on the same page: to 18% in 1982, to 19% in 1989, and to 20% in 1997, which is the rate in force.3

So the question is not what 20% of the fee comes to. It is what a year of income tax comes to with the fee in it, against the same year without it. For the designer that difference is €3,289.60 of tax, and it breaks down like this.

The second line is the one that does not appear in anybody’s mental arithmetic. Two reliefs are sized on the whole of a person’s income rather than on their salary: the employee detrazione of article 13, comma 1, which falls from €1,910 to nothing between €28,000 and €50,000, and the further detrazione of the 2025 budget law, worth €1,000 up to €32,000 and nothing at €40,000. Side income lands on top of the salary and pushes both down. Adding €6,000 to a €35,000 salary takes €625.00 of the second and €578.98 of the first.89

Where the money goes depends on the day job

Because the reliefs taper over particular stretches of income, the cost of the same €6,000 of work depends on where the salary sits. At €20,000 it is 33.5% of the fee. It climbs through the 33% band and both tapers at once, peaks at 58.1% for salaries between €32,000 and €34,000, and falls back to 46.0% once the further detrazione is exhausted and only the tax rate is left.13

In cash, that is the difference between finishing the year €730.42 short and €2,204.60 short, for identical work at identical fees.

There is one place a cliff might reasonably be expected, and there is not one. Below €20,000 of total income an employee receives a payment rather than a detrazione, and side income that carries them over €20,000 takes it away. On a €20,000 salary that is €960.00 lost — but the detrazione that starts on the other side of the line is worth €1,000.00, so a €1,000 fee still leaves €696.19. The two provisions were drafted to hand over to each other and they do.109

The €5,000 line is a contribution line

The figure most people have heard is €5,000, and it is real but narrower than its reputation. Article 44, comma 2 of a 2003 decree enrolled occasional self-employed workers in the Gestione separata “solo qualora il reddito annuo derivante da dette attività sia superiore ad euro 5.000” — only where the annual income from that work exceeds €5,000. It is a threshold for social contributions and not for tax, only the excess is charged, and the article carries no amendment to it since it took effect on 1 January 2004.4

Above the line the client pays the contribution and keeps a third of it back from the fee, under the rule that splits Gestione separata contributions one third to the worker and two thirds to the client. Someone who already has a job is insured under a compulsory scheme, which sets the rate at 24%. On the designer’s €6,000 that is €240.00 in all and €80.00 of their own money.56

Which is to say the contribution is not what makes the bill. Hold the same designer at exactly €5,000, where no contribution arises at all, and the tax still comes to €2,885.64, of which €1,885.64 is left to pay after the withholding — 57.7% of the fee, a higher share than at €6,000.12

With no other income, most of it comes back

The picture inverts for someone with no other income — a student, a person between jobs. Article 13, comma 5 grants a detrazione against this kind of income which, up to €5,500 of total income, is worth exactly the tax on it: €1,265 of relief against €1,265 of IRPEF. Below that line the income tax is nil and the withholding is refunded, apart from the regional and municipal surcharges. A €3,000 fee is withheld €600.00 and returns €533.10 of it.812

The two thresholds sit €500 apart and belong to different institutions. The contribution line is €5,000; the point at which income tax starts, for someone with nothing else coming in, is €5,500. Neither of them is a tax-free allowance for a person who already has a salary, because for them the first euro of the fee is taxed at whatever rate the salary already reached.

Documented expenses reduce the base, not the withholding

Article 71, comma 2 taxes the difference between what was received and the expenses specifically incurred to produce it, so a photographer who hires a studio for the shoot is taxed on the fee less the hire. The withholding is not adjusted for it: the client withholds on what it pays. At €6,000 with expenses of a fifth of the fee, the balance due falls from €2,089.60 to €1,572.80 — and what the person actually keeps falls too, from €2,630.40 to €2,027.20, because the money was spent.212

Where the person lives moves the figure much less than that. Taking the regional and municipal surcharges to the ends of their statutory range rather than the 2.23% average used throughout puts the balance between €1,999.02 and €2,154.72. The spread across Italian comuni is measured in a separate piece.11

What this does not settle

It does not price a salary between one euro and €20,000. In that stretch a third payment, the trattamento integrativo, is also in play and interacts with the two reliefs above; the grid starts at €20,000 rather than guess at it. Nor does it price someone with no other compulsory cover who goes over the €5,000 line, because their contribution rate is higher than 24% and is set by an INPS circolare rather than by statute. The zero-salary rows stop at €5,000, below which no contribution arises.

It also assumes the work really is occasional. That is a legal test rather than an arithmetic one: the code says non esercitate abitualmente, not carried on habitually, and repeating the same work for the same clients year after year is how a person ends up owing a partita IVA they never opened. Nothing in these numbers speaks to where that line falls.1

And the balance at the return is not always the end of it. A first liability of any size sets off the instalment machinery for the following year, which is priced in a piece on second-year cash. Paying late has its own schedule, in a piece on the June deadline.