How is the CISSM calculated in Luxembourg?

The Tax Credit for Minimum Social Wage (CISSM) is a tax assistance that aims to guarantee tax neutrality for employees receiving a salary close to the minimum social wage, particularly during part-time work or temporary reduction of working hours.

To calculate the CISSM, you must first determine a fictitious gross salary based on the declared gross salary and the ratio between theoretical hours and actually worked hours.

Calculation Method

Calculate the fictitious gross salary 

Fictitious gross salary = Gross salary × (Theoretical hours ÷ Actual hours)

Check the applicable CISSM bracket

• From 1800€ to 3000€: Fixed CISSM of 81€/month
• From 3000€ to 3600€: Decreasing amount according to the formula → CISSM = 81 / 600 × [3600 − Fictitious Monthly Gross Salary]
• No credit granted for salaries below 1800€ or above 3600€

Calculate the theoretical CISSM 

Theoretical CISSM = (81 ÷ 600) × (Bracket ceiling – Fictitious gross salary)

Prorate according to actually worked hours 

Granted CISSM = Theoretical CISSM × (Actual hours ÷ Theoretical hours)

Example

An employee receives a gross salary of 1947,50€, with 96 actual hours worked out of 168 theoretical hours for the month of August 2025.

Fictitious salary calculation:

1947,50 × (168 ÷ 96) = 3408,13€

Applicable bracket:

The fictitious gross (3,408.13€) falls between 3000€ and 3600€.

→ Theoretical CISSM of 25,90€

Theoretical CISSM calculation:

(81 ÷ 600) × (3600 – 3408,13) = 25,90€

Proration:

25,90 × (96 ÷ 168) = 14,80€

The granted CISSM for this employee will therefore be 14,80€.

Important points to remember

• CISSM guarantees an adjustment based on the fictitious gross salary.
• The calculation depends on the remuneration bracket in which the fictitious salary falls.
• The final amount is always prorated according to the hours actually worked.

Source

• ACD (Administration of Direct Contributions)

Updated on: 25/08/2025