Taxes 2026: Divorce, Marriage, Shared Custody... The 5 Pitfalls to Absolutely Avoid on Your Tax Declaration to the DGFIP

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Taxes 2026: Divorce, Marriage, Shared Custody... The 5 Pitfalls to Absolutely Avoid on Your Tax Declaration to the DGFIP

Created on 25/04/2026 at 10:02, by Joséphine de Rubercy

Taxes 2026: Have you gotten married, entered a civil partnership, separated, or changed your custody arrangement or family model in 2025? These personal events have significant tax implications. Each year, mistakes related to divorce, shared custody, or blended families are among the most common... and can cost you valuable benefits or even lead to a tax reassessment. Here are the 5 pitfalls to absolutely avoid in your declaration.

As every spring, the income tax declaration campaign is officially open. Since April 9, 2026, taxpayers can fill out their declaration online at impots.gouv.fr or send it in paper form. While the task may seem tedious (who really enjoys filling out their tax notice?), it is also crucial to avoid mistakes that could cost you dearly. This is especially true if your family situation has changed recently. Marriage, civil partnership, separation, divorce, shared custody, or blended family: these intimate events also change how you must present yourself to the tax authorities.

Number of tax shares, boxes to check, choice of joint or separate declaration, alimony... each situation corresponds to a specific box. And each year, errors in declarations related to a family change are among the most frequent, according to the DGFIP. If filled out incorrectly, some boxes can deprive you of a tax advantage, or even lead to a reassessment. As you are likely in the middle of filling out your declaration (or will be soon), we help clarify things. What are the pitfalls to avoid? How to make the right choices based on your situation? Spoiler: a changing family life does not necessarily mean bad tax surprises. We explain.

Did you get married or enter a civil partnership in 2025? This choice is crucial

If you got married in 2025, you have two options for your income tax declaration: a joint declaration or two separate declarations, according to the Public Service. This choice is not automatic and can have a significant impact on your tax amount. It is impossible to go back after validation, so compare both options carefully before confirming.

In some cases, making two separate declarations can reduce the tax bill, especially if the couple's incomes are very unequal. Depending on the situation, the savings can reach several hundred euros. To be sure of your choice, the best reflex is to test both options on the official simulator before validating. If you have already submitted your declaration, you can still correct it until the online service closes.

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Are you separated/divorced with children? Beware of these 2 very common pitfalls

In the case of divorce or separation, the number of tax shares and the boxes to check depend directly on the organization of custody and the alimony paid. Here are the cases to pay attention to and that you must report in your declaration:

• Shared custody: you cannot declare the child as your exclusive dependent. You must check the "shared custody" box: each parent then benefits from an additional half-share per child, or +0.25 share for each of the first two children, and +0.5 share for the third child. Example: with three children in shared custody, each parent gets 2 shares (1 basic share + 0.25 share for each of the first two children + 0.5 share for the third).

• Alimony: it is only deductible if the child is not declared as your dependent. In shared custody, the deduction for alimony is therefore impossible, except in very exceptional cases (specific court decision). The classic mistake? Two parents declaring the child as an exclusive dependent. Result: guaranteed reassessment.

• Single parent: If you live alone with at least one dependent child, remember to check box T to benefit from an additional half-share. Be careful, this status is not accessible if you are cohabiting.

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Blended family: the tax authorities do not always follow you (and it can cost you dearly)

New life, new home, new children... In a blended family, the declaration can become a real headache. A stepparent cannot declare a child who is not legally under their care, even if they raise them daily. Each child potentially entitles you to tax shares, provided the right person checks the right box.

An error in the allocation of shares can increase your tax bill by several hundred euros. Note: if you were a single parent with one dependent child, the blended family situation can cause you to lose a half-share or even a full share, depending on the configuration of your new household.

Taxes 2026: 5 mistakes to avoid if your family situation has changed

Marriage, breakup, death, birth, moving... Any change in situation in 2025 must be reported in the 2026 declaration, even if you are on a monthly payment plan or withholding at source. Failing to do so risks an incorrect withholding rate, a poorly calculated advance, or even an overpayment to be refunded. Above all, also update your personal space on impots.gouv.fr to adjust your withholding rate in real time. A forgetfulness can lead to an adjustment of several hundred euros in overpayment to be refunded.

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Here are the 5 mistakes to avoid in case of family change:

• Validating a joint declaration without checking if it is really advantageous
• Declaring a child as an exclusive dependent when they are in shared custody
• Deducting alimony without having the right to (in shared custody, this is impossible except for very specific court decisions)
• Misallocating tax shares in a blended family
• Forgetting to report a change in situation from 2025

Don’t panic if you make a mistake in your declaration: you can correct it until the deadline (this varies depending on your department and whether you chose the paper or online version). After that, a correction procedure remains possible until mid-December. It’s better to take care of it now: take the time to check each point, simulate, and don’t hesitate to seek information on impots.gouv.fr or from a professional to avoid bad surprises.

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