The difference between Zakat and Sadaqa

The difference between Zakat and Sadaqa lies in the nature of these actions.
While Zakat is a tax obligation for every eligible Muslim, Sadaqa is a voluntary gift that any Muslim can give in any situation and can range from a smile or a good word, as the Hadith tells us, to any other kind of help, financial or otherwise.
The word Zakat in Arabic has the meanings of growth, blessing and purification.
Zakat is a fixed percentage of the wealth accumulated during a year that has exceeded a minimum and which the Muslim is obliged to pay.
In this sense, the payment of Zakat is a purification of our wealth so that it can grow in a healthy way, like the tree that is pruned every year, and be a blessing for us in this life and the next.
The obligatory nature of Zakat is specified in the Qur’an, and its importance is demonstrated by the fact that it appears almost thirty times, connected with the command to perform the prayer:

And establish salat, give Zakat and obey the Messenger so that mercy may be given to you.
(Surah of Light, 24:56)

Zakat has its own jurisprudence that defines how to do it in order for it to be valid and accepted.
In addition, Zakat has a number of categories defined by Allah in the Quran of who can receive it.
The difference between Zakat and Sadaqa is like the difference between the five obligatory prayers, which are a pillar of Islam and have their times, requirements and conditions, and the voluntary prayers, which can be done at any time of the day and night.
The fact that we perform many voluntary prayers does not exempt us from the obligation to perform the five obligatory prayers.
The word Sádaqa comes from the root s-d-q, which is the same as sidq, sincerity.
Sadaqa is a sign of the sincerity of the believer.
Sádaqa is something that everyone, regardless of economic status, can give, and is not limited to monetary or other wealth.
Helping a person with our time or effort is Sadaqa, teaching someone something useful is Sádaqa, removing an obstacle from the path is Sádaqa, even having intimate relations with our spouses is Sádaqa.
Every action that is done with sincerity seeking to please Allah is Sádaqa.
Doing good with sincerity has no conditions, no time, no circumstances, any of them is good, nor is it specified who is to receive it.
In these verses of the Qur’an Allah does not speak of Sadaqa:

(262)
Los que gastan sus bienes en el camino de Allah y luego no lo echan en cara ni lo acompañan de ningún agravio, tendrán su recompensa junto a su Señor y no tendrán que temer ni se entristecerán.
(263)
Una palabra conveniente y perdón, es mejor que una limosna acompañada de agravio.
Allah es Rico e Indulgente.
(264) ¡Creyentes!
No hagáis que vuestras limosnas pierdan su valor porque las echéis en cara o causéis un perjuicio por ellas; como aquél que da de su riqueza por aparentar ante la gente, pero no cree en Allah ni en el Último Día.
Es como una roca sobre la que hay tierra y le cae un aguacero dejándola desnuda.
No pueden beneficiarse de nada de lo que obtuvieron.
Y Allah no guía a la gente incrédula.
(265)
Los que gastan sus bienes buscando la satisfacción de Allah y siendo una confirmación procedente de sí mismos, se parecen a un jardín frondoso y elevado sobre el que cae un aguacero y da sus frutos multiplicándose por dos; y si no le cae el aguacero tiene el rocío.
Allah ve lo que hacéis.
(266) ¿Acaso le gustaría a uno de vosotros tener un jardín de palmeras y vides por el que corrieran ríos y en el que hubiera toda clase de frutos y que siendo ya viejo y con una descendencia aún débil, viniera un torbellino de fuego y le quemara el jardín?
Así os aclara Allah los signos; ojalá reflexionéis.
(267) ¡Vosotros que creéis!
Dad de las cosas buenas que habéis obtenido y de lo que hemos hecho salir para vosotros de la tierra y no escojáis intencionadamente lo que, de ello, sea despreciable para darlo, cuando vosotros mismos no lo aceptaríais a no ser con los ojos cerrados.
Y sabed que Allah es Rico, en Sí mismo alabado.
(Sura Al-Baqarah, 2)

The content about the general meaning of giving generously in these verses can be applied to both Zakat and Sadaqa, because in a way it can be understood that giving Sadaqa has so much benefit that it could be contemplated that Allah has made Zakat obligatory to ensure that we receive a minimum share of this benefit.
But we must be clear that Sadaqa, no matter how much it is or how it is formed, will never take the place of Zakat nor can it be used as a substitute for it.
It would be like saying that because we get up to perform voluntary prayers at night, we do not have to perform the five obligatory prayers during the day.