The tredicesima: how Italy's thirteenth-month pay is calculated

One twelfth for every month worked

The tredicesima is an extra month's pay that accrues a piece at a time through the year. The piece is the twelfth: every month of service accrues one twelfth of your gross monthly pay.

gross monthly pay × months of service ÷ 12

Twelve months of work make 12 twelfths, one whole extra month of pay, which is the common case and the reason it is called a thirteenth month. Starting partway through the year accrues a fraction.

If you work part time there is no reduction to apply: the monthly pay on your payslip is already proportional to your contracted hours, so the tredicesima that follows is already the part-time one. Reducing it a second time is the most common mistake on this calculation.

The base is the qualifying pay, not everything printed on the payslip. As a rule the basic rate, the contingency allowance, the EDR, seniority increments and personal supplements count; overtime, one-off bonuses and expense reimbursements do not. Exactly which items count is set by your CCNL, the sector collective agreement.

The 15-day rule

If you were hired or left mid-month, that month is not split, it is rounded. At least 15 days worked and the month counts in full; fewer than 15 and it does not count at all.

It is a hard threshold, and the gap between the two sides is the whole twelfth:

Someone hired on the 17th of a 31-day month works 15 days and accrues the full twelfth; someone hired on the 18th works 14 and accrues nothing. One calendar day is worth a twelfth of a month's pay.

This is the convention in most collective agreements, but not all: a minority of CCNLs prorate by day, dividing by 30. There, 10 days are worth a third of a twelfth rather than zero. It is worth checking your own agreement, because the two rules differ precisely in the month you care about.

Which months accrue and which do not

You do not have to be physically at work to accrue the tredicesima: the employment relationship has to be live and the absence either paid or protected.

As a rule these accrue:

• holiday and paid leave;
• sickness, within the limit set by the CCNL;
• workplace injury;
• compulsory maternity leave;
• marriage leave;
• the wage guarantee fund, with the extra-month share carried by the INPS.

As a rule these do not:

• unpaid leave of absence;
• strike days;
• optional parental leave;
• unjustified absence;
• sickness beyond the contractual limit.

"As a rule" is not hedging: the CCNL decides, and agreements genuinely differ here. That is why the tredicesima calculator asks for the months you actually accrued rather than inferring them from a start date.

When it is paid

By Christmas. Many CCNLs name Christmas Eve as the deadline, others align it with the December payslip. In almost every case it arrives separately from the month's salary, so December shows two payments.

When employment ends during the year the twelfths already accrued are not lost: they are settled with the final payments, alongside the TFR (severance accrual) and untaken holiday.

Why the net is lower than a salary

This is the part that surprises people every December, and the explanation that circulates most is wrong. The tredicesima does not carry a higher rate. The IRPEF applied is exactly that of any other month. What is missing is a tax credit.

The employment tax credits (article 13 of the TUIR, Italy's income tax code), those for dependent family members and the trattamento integrativo are computed on the year and spread across the twelve ordinary payslips. They are not granted a second time on the additional month: there is no thirteenth twelfth of credit to apply. So the tredicesima's taxable amount is taxed "full", while an ordinary payslip's is lightened by its share of the credit.

What the tredicesima therefore pays:

1. your INPS contributions, normally 9.19% (the pension share of the Fondo Pensioni Lavoratori Dipendenti, Italy's main employee pension fund; the employer pays the other 23.81%). Above €56,224 of annual pay a further 1% applies;
2. IRPEF on what remains, at your marginal rate, with no tax credits.

The regional and municipal surcharges usually do not appear on the tredicesima payslip: they are computed on the annual total at the year-end reconciliation and withheld in instalments. The tredicesima does enter that base, so the surcharge on it is paid, just later.

The 2026 IRPEF brackets

For 2026 IRPEF has three brackets. The second rate fell from 35% to 33% with the 2026 budget law (Law 199 of 30 December 2025, article 2), which is worth knowing because several tables in circulation still show 35%.

Note how these read: crossing €28,000 does not retax the whole income at 33%. The higher rate applies only to the part above the threshold, and one euro past the boundary costs 33 cents, not two thousand euro.

This matters more for the tredicesima than for a salary, because the tredicesima is added to the year's income and can land across a bracket boundary: part taxed at 23% and the rest at 33%. Applying a single rate to the whole amount, as most online tables do, gives a wrong figure in both directions.

A full example

Take €2,000 gross a month, a full year.

That leaves 69.92% of the gross: deductions are 30.08%.

Now €2,500 gross a month, again a full year. The taxable income from the ordinary payslips is €27,243, still inside the first bracket, but the tredicesima's taxable amount (€2,270.25) carries it to €29,513.25. Part of the tredicesima is therefore taxed at 23% and the rest at 33%: the IRPEF is €673.48 and the net €1,596.77, so 36.13% is withheld. A thousand euro more of monthly pay and the share that survives falls by six points, purely through the bracket.

From the gross to your own number

The formula is simple, the variables are not: the months you actually accrued, how your CCNL counts the month you were hired, your contribution rate, the bracket your year lands in. The tredicesima calculator puts them together and shows every line from gross to net, including the IRPEF worked out as the difference between the tax with and without the additional month.

If the tredicesima is money you intend to put aside, compound interest shows what a sum paid in once a year becomes over several years. And if you just want to reason about percentages on a payslip, the percentage calculator does it in one step.