Precisar vs. necessitar
Both precisar and necessitar translate to to need in English, but they are not always interchangeable. The main difference lies in their formality, frequency of use, and the intensity of the need they express.
Precisar
A1This is the most common and versatile word for to need in both spoken and written Portuguese. It covers a wide range of everyday needs, from simple wants to important requirements. It is often followed by the preposition de when needing an object or person, or used directly before another verb.
Eu preciso de um carro novo.
(I need a new car.)
Você precisa terminar o relatório até amanhã.
(You need to finish the report by tomorrow.)
Nós precisamos de ajuda com a mudança.
(We need help with the move.)
Ela precisa de mais tempo para pensar no assunto.
(She needs more time to think about the matter.)
Preciso ir ao supermercado depois do trabalho.
(I need to go to the supermarket after work.)
As crianças precisam de um ambiente seguro para crescer.
(Children need a safe environment to grow.)
Necessitar
B1This word also means to need but is significantly more formal and less common in daily conversation. It implies a more profound, fundamental, or urgent need, often one that is essential for survival, function, or compliance. Necessitar is almost always followed by the preposition de.
O corpo humano necessita de água para sobreviver.
(The human body is in need of water to survive.)
A organização necessita de doações para continuar seu trabalho humanitário.
(The organization is in need of donations to continue its humanitarian work.)
O paciente necessita de cuidados médicos imediatos.
(The patient is in need of immediate medical care.)
Para a matrícula, o aluno necessita de apresentar toda a documentação.
(For enrollment, the student needs to present all the documentation.)
A indústria necessita de uma reforma estrutural para ser competitiva.
(The industry is in need of a structural reform to be competitive.)
Muitos filósofos acreditam que a alma necessita de arte e beleza.
(Many philosophers believe that the soul needs art and beauty.)
Summary
In short, use precisar for almost all everyday situations where you want to say to need. Reserve necessitar for more formal contexts, such as official documents, academic writing, or when you want to emphasize a deep, critical, or fundamental need. While they can sometimes be interchangeable, precisar is the default and more natural choice in conversation.