You have just divorced, your children have left the tax household, and when filling out your tax return, you come across box L without really knowing if it applies to you. This situation affects thousands of taxpayers every year who miss out on an additional tax share simply because the distinction between box T and box L remains unclear.
Box L and box T on the tax return: two provisions for different situations
People often confuse these two boxes, and it makes sense: both target single parents. The T box concerns parents who are raising a child alone who is still dependent. You check T as long as your minor child (or dependent adult) lives under your roof and you are solely responsible for their upkeep.
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Box L, on the other hand, is aimed at a different profile. It concerns individuals who have raised a child alone for at least five years, but whose child is no longer part of the tax household. The child has grown up, moved out, is filing their own return, and you find yourself alone with no one dependent.
To understand how to declare a single parent and box L on taxes, you must remember this key criterion: box L is only activated when the child has left the tax household, not before.
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The five years required do not need to be consecutive. Recent tax doctrine specifies that periods of primary custody alternating with shared custody can be counted, as long as the parent has effectively taken on the primary upkeep alone during those periods.
Living alone condition for box L: what the administration really accepts
The biggest hurdle for many taxpayers is the notion of “living alone.” It is commonly thought that sharing a home with someone automatically disqualifies you. It’s not that simple.
Since the 2025-2026 campaign, the administration has provided clarification that changes the game for many situations: neutral cohabitation does not disqualify you from box L. Sharing an apartment with a friend, a family member, or a roommate, without a couple’s living arrangement, remains compatible with the status of a single parent. The condition is that everyone has separate expenses and that the taxpayer remains single, divorced, separated, or widowed.
What disqualifies you is marital life, cohabitation in a recognized partnership, or a civil partnership. If you are living with a partner without being married or in a civil partnership, you cannot check box L, even if your situation is not officially recognized.
Common situations that raise questions
- You are hosting your elderly mother at your home: family cohabitation without a marital link does not affect box L, as long as there is no couple’s life
- Your adult child temporarily returns home between two residences: if they are no longer fiscally dependent, box L remains valid
- You have a new partner who regularly sleeps over without officially living there: responses vary on this point, but the administration looks at the reality of cohabitation, not just the postal address
Adult child not dependent: the trap of alimony
Many parents continue to financially support their child after they leave the tax household. Payment of alimony, help with rent, covering tuition fees. The question often arises: do these aids jeopardize the right to box L?
The answer is no. The DGFiP has clarified that an adult child who is no longer dependent (because they have their own partner or child, or simply because they are filing their own return) is indeed counted as “no longer dependent,” even if the parent is providing significant amounts. The maintenance of alimony or housing assistance does not jeopardize the L share.
This clarification is included in the Official Bulletin of Public Finances-Taxes (BOFiP). It resolves a doubt that many taxpayers have carried for years.
What to check before ticking box L
- Your child is no longer dependent on your tax household (they are filing their own return or are dependent on another household)
- You have raised this child alone for at least five years, consecutive or not
- You are single, divorced, separated, or widowed as of January 1 of the tax year
- You do not live in a cohabitation or common-law partnership with a partner
Common mistakes on the single parent tax return
The first mistake is checking box T when you should check box L. If your last child has left the tax household but you meet the five-year conditions, box L entitles you to an additional half-share for life. Box T, on the other hand, is no longer applicable when there are no dependent children.
The second common mistake: not checking anything at all. Many taxpayers think that the additional half-share disappears with the child’s departure. This is false; box L exists precisely to maintain this tax advantage.
The third trap: checking box L in the year of separation. In the year of divorce or civil partnership dissolution, it is box T that applies if you have a dependent child, not box L. Box L takes over only when the child leaves the tax household.
The pre-filled return does not automatically check these boxes. It is up to the taxpayer to do so manually, in the “tax household situation” section (frame A or B depending on the form). An oversight, and the half-share is lost without warning from the administration.