Inheritance Law2026-10-22

My father had dementia when he wrote his will — does that make it invalid?

Dementia does not automatically invalidate a will. I explain when a person truly lacked testamentary capacity, how you prove it, and the route by which you can raise it.

You have read your father’s will and something is not right: a stranger stands to benefit, a child is passed over, a provision makes no sense. You know that in his final years he suffered from dementia. And so you ask yourself whether the will is simply void.

In short

No — not automatically. A diagnosis of dementia on its own does not make a will invalid. What matters is your father’s state of mind at the moment he signed it. He had to be able to understand the meaning of what he was declaring and to form his wishes freely on that basis. The burden of proving otherwise falls on whoever claims the will is invalid. In practice, most cases founder on precisely that question of proof, not on the law itself.

How I can help

Assessing whether, given the particular course of the illness, there is any realistic prospect of proving a lack of testamentary capacity
Obtaining and reviewing care records, medical correspondence and guardianship files
Commissioning a specialist medical report on testamentary capacity at the decisive point in time
Representing you in the certificate of inheritance proceedings before the probate court, or in a declaratory action
Negotiating with the other heirs where a settlement reaches the goal faster than years of litigation

What a lack of testamentary capacity means in law

§ 2229(4) of the German Civil Code (BGB) sets out who cannot make a valid will. A person is excluded if, because of a pathological disturbance of mental activity, because of mental deficiency or because of a disturbance of consciousness, they are unable to appreciate the meaning of the declaration they are making. The same applies where the person cannot form their wishes freely in accordance with that appreciation.

These are two distinct abilities. On the settled interpretation, both need not be impaired at the same time. It is enough that one of them is missing.

The ability to understand — the testator must grasp what a will is and what it does. They must also be able to gauge the consequences of their specific arrangements for their estate and for their family.
Freedom of decision — they must be able to translate that understanding into a genuine decision of their own, not one steered from outside.

A diagnosis of dementia describes a progressive decline in mental faculties. In itself, though, it says nothing about the particular state of mind on the day the will was made. In the early and middle stages, the ability to understand and to exercise judgement often remains intact for a long time, even where memory or orientation are already markedly impaired. What counts, then, is not the label “dementia” but the degree and severity of the illness at the relevant moment.

The only moment that counts

The decisive moment is the making of the will and nothing else — not the state of mind years earlier when the diagnosis was given, and not the state of mind years later at death. That holds true even where the illness as a whole is progressive and irreversible. People with dementia frequently have what are known as lucid intervals, periods of hours or even days in which their mental faculties are far clearer than at other stages of the illness. A will made during such a lucid interval can be valid — even if the testator was considerably confused shortly before or after.

For the purpose of proof this means that general statements such as “he had been demented for years anyway” take you nowhere. What you need are points of reference as close as possible to the date the will was made — care notes, medical appointments, medication charts or observations by witnesses from the immediate period around the signing.

Voidness rather than challenge — why this is decisive for your time limit

This is the most common misunderstanding I encounter in practice: clients assume they must “challenge” the will within a year. That is indeed the position with mistakes or threats under § 2078 BGB, where the time limit for challenge follows from § 2082 BGB. Where testamentary capacity is in question, the assumption is wrong.

If the testator lacked capacity when the will was made, the will is void from the outset. It never takes legal effect at all. No act of challenge is needed. The one-year period under § 2082 BGB does not run. In principle you can therefore still raise the invalidity years later. The condition is that the inheritance matter has not yet been finally settled — which is the case, for example, where no certificate of inheritance has yet been issued, or where the one issued can still be contested. That gives you more time than many people assume. It does nothing, however, to change the fact that the evidence grows weaker with every passing year. Witnesses remember less, and documents disappear.

How you raise and prove the lack of testamentary capacity

There are two routes. On both, it is the court that examines the question:

1. Certificate of inheritance proceedings before the probate court (§ 352e FamFG). Where someone applies for a certificate of inheritance on the basis of the will, the probate court examines the underlying facts. It issues the certificate only where it regards those facts as established. If you dispute testamentary capacity, the court must look into that question. Here the principle of investigation of its own motion applies, under § 26 FamFG: the court establishes the facts of its own accord. It is not confined to what the parties put forward. It may, for instance, commission an expert report itself.

2. Declaratory action. Where a certificate of inheritance has already been issued, or where clarification is urgent for other reasons, a declaratory action may be the way forward. With it you obtain a ruling that the will is invalid for want of testamentary capacity.

In both cases the same rule applies: whoever asserts the lack of testamentary capacity bears the burden of proving it. This is the greatest hurdle in practice. The evidence that carries weight includes:

Care records from a residential or domiciliary care provider around the date the will was made
Test results such as the MMSE (Mini-Mental State Examination), where carried out close to the time
A specialist medical report from neurology or psychiatry — ideally prepared retrospectively on the basis of the available documents where no contemporaneous examination exists
Witnesses who saw the testator during the period in question — care staff, the family doctor, neighbours, other relatives

If the will was recorded by a notary, that is no clean bill of health. Under § 11 BeurkG the notarial form is only an indication of legal capacity. Where a notary is convinced that capacity is absent, they are required to refuse to record the will. Where they merely have doubts, the position is different: they are not convinced of any defect in capacity, only uncertain. In that case they note the doubts in the record and go ahead with recording it all the same. The absence of any note of doubt in the record is no proof of testamentary capacity. It shows only that, on that day, the notary was neither convinced of an absence of legal capacity nor in doubt about it. With insidiously progressing dementia in particular, even notaries miss the true state of affairs where the conversation is brief and unremarkable.

A typical case from my practice

A testator makes a new will at an advanced stage of his illness. It disinherits one child entirely and benefits a carer — a carer who had come into the house only a few months earlier. The care records from the period in question describe recurring episodes of confusion, difficulties with orientation and a growing susceptibility to influence by others. A retrospective specialist report, drawing on these documents and on supplementary witness evidence, concludes that during the relevant period free formation of the testator’s wishes was no longer possible. On that footing, the lack of testamentary capacity can be made out in the certificate of inheritance proceedings. Without such a report and without contemporaneous documentation, the very same suspicion remains mere assertion.

Common mistakes

Arguing from the diagnosis alone. “He had dementia” is no substitute for a report on his actual state of mind on the day the will was made.
Fearing a one-year time limit that does not apply here. Those who believe they must “challenge” within a year often give away time — time they could have used for a thorough gathering of evidence.
Starting to secure the evidence too late. Care notes are destroyed and witnesses forget detail — the longer you wait, the thinner the evidence becomes.
Treating the notarial recording as a clean bill of health. It is an indication, not proof.
Commissioning a report before the documents have been reviewed. Without care records and a connection in time to the date the will was made, even the finest expert cannot produce a conclusion that holds.

Frequently asked questions

Is a medical diagnosis of “moderate dementia” enough as proof?

No. The diagnosis describes the general course of the illness, not the actual state of mind on the day the will was made. What matters is an assessment tied to precisely that moment, supported by documentation and, where appropriate, an expert report.

What happens if the will is declared invalid?

Then either an earlier, still-valid will applies. If no other will exists, the statutory order of succession applies. In an individual case that outcome may not automatically be to your advantage, even as the person contesting the will — so have it assessed beforehand.

Do I have to act at once if I have doubts?

In law there is no short time limit of the kind that applies to a challenge. In practice you should nonetheless start early. Care records are destroyed once the statutory retention periods expire, and witnesses recall specific detail less well as time passes.

What if there is no contemporaneous medical report?

That is the normal situation, not an obstacle. A specialist in neurology or psychiatry can, even after the event, prepare a retrospective assessment of testamentary capacity for the period in question on the basis of the available documents — care records, medical correspondence, medication charts and witness accounts.

Can I still raise the lack of testamentary capacity once a certificate of inheritance has been issued?

Yes — a certificate of inheritance that has already been issued does not, as a matter of principle, rule out a declaratory action. It does, however, make the procedural position more complex, which is why you should not take this step without a legal assessment.

Your next step

Whether a suspected lack of testamentary capacity can actually be proved turns on the quality of the documents available. And that quality grows worse with every month, not better. Let me assess the care records, the medical documents and how close they sit in time to the date the will was made, before you begin proceedings or resign yourself to the succession as it stands. I act for clients throughout Germany, by telephone or video, in certificate of inheritance proceedings as in declaratory actions. You can find more on this area in inheritance law. Get in touch for a first assessment of the prospects of success in your case.

This article provides general information and is no substitute for legal advice in an individual case. Last updated: 2026-10-22.

Christian Czirnich, Rechtsanwalt (attorney at law), Kirchseeon near Munich

Describe how your father seemed when he signed – I will look into it.

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