Can non-Muslims give zakat?

Why zakat is only for Muslims

Zakat is one of the five pillars of Islam, like prayer and fasting. It needs faith and an intention to obey Allah, so it only becomes a duty after someone accepts Islam. When the Prophet ﷺ sent Mu'adh to Yemen, he told him to invite people to the testimony of faith first, then prayer, and only after that to tell them about zakat (Sahih al-Bukhari 1395). Belief comes first; zakat builds on it.

This is not a judgement about anyone's generosity. A non-Muslim can't "pray salah" on someone's behalf in the Islamic sense either. It is simply how acts of worship work.

So what is a non-Muslim's donation?

It is charity, and Muslim charities happily accept it into their general or emergency funds. The Quran says that no good deed is lost:

Charities usually keep zakat in a separate pot, because it can only go to the eight Quranic categories. A non-Muslim's gift doesn't have those limits, so it can fund anything from wells to school books. Practically, just choose the "general donation" or "sadaqah" option on the form. See What is the difference between zakat and sadaqah?

If you're thinking about becoming Muslim

Good you did before Islam is not wasted. Hakim ibn Hizam asked the Prophet ﷺ about the charity and kindness he had done before Islam, and he replied, "You embraced Islam with all the good you did before" (Sahih al-Bukhari 1436). So giving now, before you become Muslim, still counts in your favour.

Zakat itself starts only after you become Muslim, once your savings pass the nisab threshold and a lunar year goes by. You don't owe anything for the years before. See Do I have to pay zakat as a new Muslim?

The other way round

A different question is whether Muslims can give their zakat to non-Muslims. Most scholars say zakat goes to Muslims, while voluntary charity can go to anyone. See Can I give zakat to non-Muslims?