Caducar vs. expirar vs. vencer

The Spanish words 'caducar', 'expirar' and 'vencer' often can be used interchangeably as they all refer to something 'coming to an end' or 'becoming invalid'. However, each term tends to be used in different contexts and carries its own nuances.

Caducar

'Caducar' is often used when referring to legal permissions, rights or licenses coming to an end. It can also refer to perishables that have gone past their consumable date.
La patente del medicamento ha caducado.
(The patent for the medicine has expired.)
Este contrato va a caducar dentro de dos días.
(This contract is going to expire in two days.)

Expirar

'Expirar' shares similarities with 'caducar', but it is usually associated with expiration in a more general sense, often used when something naturally comes to an end or ceases. This term can frequently be seen in contracts or deadlines context.
El plazo para entregar la tarea ha expirado.
(The deadline for submitting the assignment has expired.)
Su membresía anual está a punto de expirar.
(Your annual membership is about to expire.)

Vencer

While 'vencer' also means 'to expire', it is frequently associated with defeating someone or something. It will be used typically related to expiration of documents, contracts, competition or challenges.
La visa de Ana vence el próximo mes.
(Ana's visa expires next month.)
Nuestro equipo venció al adversario en el partido de ayer.
(Our team defeated the opponent in yesterday's match.)

Summary

'Caducar', 'expirar', and 'vencer' all have expiration as a theme in their definitions but are each utilized more commonly in specific scenarios. While their usage can occasionally overlap, understanding these nuances can help offer precision and color in Spanish conversation or writing.