France: three different "net" figures on one payslip
A French payslip does not have one net figure, it has several, and they are all correct. Salaire brut is the headline. Take off the pension contributions, the complementary AGIRC-ARRCO pension, CSG and CRDS and you get net avant impot, the amount that used to land in your account. Take off the income tax withheld at source and you get net a payer, what actually arrives now.
The wrinkle is CSG. It is 9.20% of pay, but only 6.80% of it reduces your taxable income; the other 2.40%, plus the 0.50% CRDS, do not. So your net imposable is higher than your net pay, by exactly those two contributions. It is also charged on 98.25% of pay rather than on all of it, up to four times the social security ceiling, above which the abatement stops.
Income tax then runs on the quotient familial: your taxable income is divided by your number of parts, the barème is applied, and the result multiplied back. Children buy parts, but the advantage each half-part gives is capped, so beyond a point another child changes nothing. A décote wipes out small tax bills and tapers away at 45.25%, and anything under 61 euro is not collected at all. One cliff worth knowing: the CET contribution is charged on the whole of your pay, but only once you pass the ceiling, so it appears in full the moment you cross it.
Pension €2,920, complementary pension €1,604, and CSG with CRDS
€3,812.10 on a base of €39,300, which is 98.25% of pay.
After the 10% professional-expenses abatement of €3,280.36, taxable income is
€29,523. The barème gives €1,971.53, less a décote of €4.88.
Take-home: €29,696.90 a year, €2,474.74 a month. Your employer pays €11,168 on top, so the job costs €51,168.