Thirteenth-Month Pay Calculator
Calculator
Thirteenth-Month Pay Calculator
From gross to net thirteenth-month pay (tredicesima): INPS contributions, IRPEF withholding with the monthly brackets and the portions accrued during the year
The calculator estimates the thirteenth-month pay of an employee: INPS contributions paid by the employee 9.19%, IRPEF brackets 23% up to €28,000, 33% from €28,000 to €50,000 and 43% above (art. 11 TUIR). The withholding on the thirteenth-month pay is calculated with these brackets divided by 12 (art. 23, paragraph 2, letter b, DPR 600/1973), without employee tax credits; the regional and municipal surcharges are not withheld. At year end the conguaglio (year-end tax adjustment) recalculates the tax on the income of the whole year, so the actual IRPEF on the thirteenth-month pay depends on total annual income. Accrual is calculated in twelfths: how a fraction of a month counts (normally 15 days) is set by your CCNL. This is an informative estimate: for your payslip the reference remains your labour consultant, CAF or patronato.
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How the thirteenth-month pay calculation works
The thirteenth-month pay (tredicesima) accrues month by month and almost all collective agreements have it paid in December. Those receiving it for the first time are often surprised: the gross amount is that of a normal salary, but the net amount in the account is noticeably lower. This calculator shows why, line by line.
You can enter either the annual RAL (gross annual salary) or the gross monthly salary: the calculator reconstructs the other figure using the monthly payments in the contract (13 or 14). The third field is the months worked, for the accrued portions of those who were hired or left the company during the year. The calculation takes place in your browser: no data is sent or saved.
The data used in the calculation
| Item | Value | Reference |
|---|---|---|
| INPS contributions paid by the employee | 9.19% of gross | IVS rate, Employees' Pension Fund |
| IRPEF — first bracket | 23% up to €28,000 | art. 11, paragraph 1, TUIR |
| IRPEF — second bracket | 33% from €28,000 to €50,000 | art. 11 TUIR, reduced from 35% by L. 199/2025 |
| IRPEF — third bracket | 43% above €50,000 | art. 11, paragraph 1, TUIR |
| Accrual | 1/12 of a monthly payment for each month worked | typical CCNL provision |
| IRPEF withholding on the thirteenth-month pay | annual brackets divided by 12: 23% up to €2,333.33, 33% up to €4,166.67, 43% above | art. 23, paragraph 2, letter b, DPR 600/1973 |
| Employee tax credits | not applied to the thirteenth-month pay | art. 23, paragraph 2, DPR 600/1973 |
| Regional and municipal surcharges | not withheld from the thirteenth-month pay | art. 50 D.Lgs. 446/1997 and art. 1 D.Lgs. 360/1998 |
The least intuitive step is IRPEF. On additional monthly payments the employer calculates the withholding “by scaling the corresponding annual income brackets to a monthly basis” (art. 23, paragraph 2, letter b, of DPR 600/1973): the thirteenth-month pay is taxed on its own, with the annual brackets divided by 12 and without tax credits. If its taxable amount exceeds €2,333.33 (€28,000 divided by 12), the excess is withheld at 33%, and above €4,166.67 at 43%. This is the calculation this tool performs.
The December withholding, however, is a provisional withholding. With the year-end conguaglio (by 28 February of the following year, or at the end of the employment relationship: art. 23, paragraph 3) the employer recalculates the tax on the income of the whole year, with the annual brackets and the tax credits due. The actual IRPEF on the thirteenth-month pay therefore depends on total annual income: if the taxable income for the year exceeds €28,000, the December withholding may be lower than the tax due and any difference is paid at the conguaglio.
Why the net thirteenth-month pay is lower than a normal monthly payment
The answer lies in two payslip lines that do not appear on the thirteenth-month pay. The first is the employee tax credits: art. 23, paragraph 2, of DPR 600/1973 provides for them on emoluments “paid in each pay period”, while the following letter, dedicated to “additional monthly payments and compensation of the same nature”, does not refer to them. They remain an annual amount that does not increase because the thirteenth-month pay arrives: that monthly payment therefore bears the full IRPEF, without the discount that lightens the other twelve.
The second is the regional and municipal surcharges, which are not withheld from the thirteenth-month pay. The advantage is only apparent: they are calculated at the conguaglio on the total income for the year — thirteenth-month pay included — and withheld in instalments over the following months.
Calculation example
Three typical cases, with the figures produced by the calculator itself:
| Item | RAL 30,000 × 13, full year | RAL 40,000 × 13, full year | RAL 30,000 × 13, 7 months |
|---|---|---|---|
| Gross monthly (RAL / 13) | €2,307.69 | €3,076.92 | €2,307.69 |
| Accrued portions | 12/12 | 12/12 | 7/12 |
| Gross thirteenth-month pay | €2,307.69 | €3,076.92 | €1,346.15 |
| INPS contributions 9.19% | − €212.08 | − €282.77 | − €123.71 |
| Taxable income | €2,095.62 | €2,794.15 | €1,222.44 |
| IRPEF withheld (monthly brackets) | − €481.99 | − €688.74 | − €281.16 |
| Net thirteenth-month pay on the payslip | €1,613.62 | €2,105.42 | €941.28 |
| Withholding rates | 23% | 23% up to €2,333.33, 33% on the rest | 23% |
With a RAL of €40,000 the gross thirteenth-month pay is 33.33% higher and the net on the payslip 30.48% higher: the taxable amount of the thirteenth-month pay, €2,794.15, exceeds €2,333.33 and the €460.82 above the threshold is withheld at 33% (€152.07), the rest at 23% (€536.67). Out of €100 gross, €69.92 remains in the first case and €68.43 in the second. The taxable income for the year, €36,324, however falls in the 33% bracket: at the conguaglio the tax is recalculated on annual income and the difference compared with the December withholding may be withheld then.
An intermediate case clarifies the mechanism: with a RAL of €35,000 the thirteenth-month pay is worth €2,692.31 gross and €2,444.88 taxable. The first €2,333.33 is withheld at 23% (€536.67) and the remaining €111.55 at 33% (€36.81), for a withholding of €573.48 (average rate of 23.46%) and a net amount on the payslip of €1,871.41. With a RAL of €32,000, instead, the taxable amount of the thirteenth-month pay (€2,235.32) stays below the monthly threshold and the withholding is all at 23%, even though the income for the year exceeds €28,000.
One last comparison, with an ordinary monthly payment. On a RAL of €30,000 over 13 monthly payments, with no dependants or surcharges, the net salary calculator estimates €24,021.40 net per year: after subtracting the €1,613.62 of thirteenth-month pay, €1,867.32 per month remains. The thirteenth-month pay is worth €253.69 less, for the same gross.
When the result should be taken with a grain of salt
Accrual in twelfths is the general rule, but the details are set by your CCNL (national collective labour agreement): most contracts count a fraction of 15 days or more as a full month and reduce the accrued portions for unpaid periods. The calculation base also varies: some contracts include superminimums or fixed allowances. On the tax side, dependants, the trattamento integrativo (supplementary payment), tax wedge measures, bonuses and fringe benefits are not considered. The 9.19% is the ordinary rate and rises to 9.49% with entitlement to extraordinary wage guarantee fund (cassa integrazione straordinaria); neither the contribution ceiling nor the additional 1% rate above a certain threshold, which concern high incomes, are modelled. This is an informative estimate, not a payslip: for your payslip the reference remains your labour consultant, CAF or patronato.
Frequently asked questions
How is the net thirteenth-month pay calculated?
You start from the gross thirteenth-month pay, equal to one twelfth of the monthly payment for each month worked: for a full year it is the RAL divided by the monthly payments in the contract. From that gross amount the INPS contributions paid by the employee (9.19%) are deducted, giving the taxable income. On that, the employer withholds IRPEF with the annual brackets divided by 12 (23% up to €2,333.33, 33% up to €4,166.67, 43% above) and without tax credits, as art. 23 of DPR 600/1973 provides for additional monthly payments. At year end the conguaglio recalculates the tax on the income of the whole year.
Why is the net thirteenth-month pay lower than a net monthly salary?
Because employee tax credits are not applied to the thirteenth-month pay: art. 23 of DPR 600/1973 provides for them on the emoluments of each pay period, not on additional monthly payments. That monthly payment therefore bears the full IRPEF, calculated with the annual brackets divided by 12. With a RAL of €30,000 over 13 monthly payments the difference is about €254.
How many months do you need to work to get the full thirteenth-month pay?
Twelve: the thirteenth-month pay accrues in twelfths, so someone who works seven months receives 7/12 of it. Fractions of a month follow the rules of the CCNL, which in most contracts counts a fraction of 15 days or more as a full month. If you leave the company during the year, the accrued portions are paid with the last payslip.
Are INPS contributions and surcharges paid on the thirteenth-month pay?
Contributions yes: the thirteenth-month pay is taxable pay for social security purposes, so the 9.19% paid by the employee is withheld as on an ordinary monthly payment. The regional and municipal surcharges, instead, do not appear on that payslip: they are determined at the conguaglio on the total income for the year and withheld in instalments the following year.
Related tools: the net salary calculator for ordinary monthly payments, the RAL from net salary calculator for the reverse calculation and the TFR calculator.
