When the tax authorities pre-fill your declaration, they can make mistakes: forgotten income, undeducted charges, missing tax credits, real costs, donations to associations, etc. A poorly checked box can cost you several hundred euros or trigger an audit.
Discover the most common errors to correct before clicking “validate”. This year, 40 million French taxpayers will complete their tax declaration form provided by the General Directorate of Public Finances (DGFiP). Of course, the document is pre-filled but it is still necessary to check certain important figures.
Income error
Before clicking on “validate”, take the time to check if the figures indicated in the box dedicated to income correspond to your salary.
Remember that the information pre-filled by the tax authorities is actually provided by your bank or employer. There may therefore be errors: an empty box if the third party concerned has exceeded the deadline or wrong figures.
Missing tax credits
Next, check carefully whether any tax credits are missing depending on your situation. In addition to the classics corresponding to personal services (50% of expenses incurred within the limit of a ceiling which varies between €12,000 and €20,000 per year) and the costs of childcare outside the home (50% of expenses incurred, within the limit of €3,500 per child or €1,750 per child in alternate residence), the arrangements MaPrimeRénov and Loc’Avantages are once again accessible following the promulgation of the 2026 finance law.
For the first, the amount varies depending on income and the region of the home concerned. But, be careful, since January 1, 2026, wall insulation and biomass boilers are no longer funded. By renting accommodation at a rent lower than the market price, the system Loc’Advantages allows you to benefit froma tax reduction of 15 to 65% according to certain criteria.
The T box
Please note, this famous T box must be checked every year, even if your situation as a single parent has not changed since the previous year. It gives the right to a tax advantage to the parent who raises a dependent child alone by increasing the number of family quotient tax shares in the household, which modifies the calculation of the amount of income tax, namely an additional half share.
Donations to associations. Be careful if you have made donations to associations during 2025 because not all are in the same boat when it comes to taxation. If it helps people in difficulty, 75% of the donation amount is deductible. Box 7UD will then be affected.
If it is an association of general interest or works recognized as being of public utility (box 7UF), a candidate for a political party (box 7UH), or a foundation for the preservation of religious heritage (box 7UJ), the deduction percentage is 66%.
Undeducted charges
The most common error in charges is alimony, check the corresponding boxes carefully depending on whether you pay or receive it. In the first case, it is entered in the “deductible expenses” section, and more precisely in one of the dedicated boxes, 6EL-6EM or 6GU.
If you perceive alimony (or that one of the members of the tax household receives one, including a minor child in your care or an adult child attached to the household), the latter is in the “Salaries, wages, pensions, annuities” section, in one of boxes 1AO, 1BO, 1CO or 1DO. It’s up to you to check if the amount is correct.
Error on professional expenses
Each year, it is possible to deduct your professional expenses either via the 10% flat rate or by counting their actual and justified amount. If the standard deduction of 10% is calculated automatically, it is applicable to all employees who do not request it and between €509 and €14,555 for income received in 2025.
But, be careful, it may be interesting to do the calculation if you estimate that your professional expenses are greater than the amount of the 10% deduction with regard to transport costsvehicle costs, additional food costs, dual residence costs, education and training costs, and telecommuting costs.
To be deductible, these expenses must be necessary for your profession, be paid during the year 2025 and be justified (keep your invoices).
