At 18, your child in principle becomes a full taxpayer. But if he continues his studies or does not yet have sufficient income To provide for his needs alone, you still have the choice: attach him to your tax household, or let him file his own declaration and deduct from your income the alimony you pay him. Both options are exclusive. An adult child can, under conditions, remain attached to your tax household until the age of 21 without proof, or up to 25 years of age if he or she is pursuing studies.
Each year, at the declaration, it is therefore necessary decide for each adult childand to do this, make the right calculations. “It’s a subject that comes up often”explains Nahima Zobri, tax lawyer and head of the tax department at Dougs. “We must first understand that legislation allows us to make choices. Optimize according to your situationthat’s not a bad thing. » On the contrary: depending on your level of income and the situation of the child, the difference between the two options can represent several hundred, or even several thousand euros of less or more tax.
Parenting your adult child: what are the advantages?
Each adult child attached represents an additional half-share of the family quotient, and even a full share from the third child attached. If you opt for attachment, your child no longer has to make a personal declaration, but his income is added to yours. You can still deduct tuition. And if he receives a salary by working in the summer for example, the income earned from an activity carried out during studies or school holidays is tax exempt within the limit of 5,405 euros (three times the monthly minimum wage, for 2025 income declared in 2026). Internship bonuses are exempt up to an annual minimum wage, or 21,621.60 euros for 2025 income.
The maximum tax saving linked to this half-share is capped at 1,807 euros. But there may be a downside: if your child receives income above these limits, you will have to include it in your own return, and your tax will increase accordingly. “We must pay attention to this does not increase your tax »summarizes Nahima Zobri
Cases where detaching your child is more favorable
If the attachment only saves you 11% (low marginal bracket), Nahima Zobri says it clearly: “There, the calculation is worth doing”. Because, if you renounce the attachment, the child must make his own declaration and you can deduct from your taxable income the pension that you pay him. Two calculation options are available to you. First option: if the child lives at your homeyou can deduct a flat rate of 4,075 euros per yearwithout any proof. This package covers accommodation and food. It is doubled to 8,151 euros if the child is married, in a civil partnership or responsible for a family, provided that you provide for his or her needs alone.
Second option: the deduction of actual expensescapped at 6,855 euros per child per year. There, it is necessary to keep all the supporting documents (rent receipts, school fees, health bills, etc.) to present them in the event of an inspection. For Nahima Zobri: “If we pay rent of 500 euros, that’s already 6,000 euros with proof. In general, we are below the threshold when the child lives with his parents. » The administration also considers that the child must be in need, living with less than 12,000 euros of annual income.
How to decide?
How to decide between the two options? It all depends on your TMI and whether the child lives with you or not. If you have proof and pay him alimony of 6,855 euros deducted at 30%, the tax saving amounts to 2,057 euroswhich is more than the ceiling of 1,807 euros for the half share. At TMI 41%, the calculation is even more favorable, with 2,810 euros in savings. And at 45%, we reach 3,085 euros. For Nahima Zobri: “When you are heavily taxed and have supporting documents, the pension option is very profitable”. In addition, tax detachment simplifies the procedures if the child wants to apply for their own social assistance (APL, activity bonus, etc.). However, attachment remains preferable from the third child, since it gives the right to a full share, or if the child lives with you. “We have to ask ourselves the question, and above all, ask ourselves and do the calculations »insists our expert.
