Short answer
Yes. Congratulating people on the arrival of Ramadan is good, and the Prophet ﷺ himself gave his Companions the good news of a blessed month. Ramadan Mubarak (a blessed Ramadan) is the most common greeting. Ramadan Kareem (a generous Ramadan) is also fine in the view of most scholars, though a few preferred other words.
Greeting and congratulating one another at the start of Ramadan is permissible and good. The sunnah has no fixed wording, so any good words are fine. Non-Muslims may also greet Muslims this way.
The four schools agree on this.
Explanation
The Prophet ﷺ told his Companions: Ramadan has come to you, a blessed month, in which Allah has made fasting obligatory on you. Scholars took from this that giving one another the good news of Ramadan is a good practice, and the early Muslims congratulated each other on its arrival.
Common greetings:
- Ramadan Mubarak: a blessed Ramadan to you. It echoes the words of the hadith.
- Ramadan Kareem: a generous Ramadan.
- Happy Ramadan or have a blessed Ramadan: plain English, and fine.
- Replies such as Allahu akram (Allah is more generous) or Khair Mubarak are customary in some cultures.
About Ramadan Kareem. A few scholars disliked this phrase because the month itself does not give anything; it is Allah who is generous in it. Most scholars see no problem, since Arabic often describes a time as generous or blessed because of what Allah gives in it, just as the Quran calls itself noble. If you prefer to avoid the debate, say Ramadan Mubarak.
Can non-Muslims say it? Yes. Muslims appreciate a colleague or neighbour wishing them Ramadan Mubarak. A kind greeting, and not eating in front of fasting colleagues where you can avoid it, are both welcomed.
When Ramadan ends, the greeting becomes Eid Mubarak. See Eid dates.
The evidence
Quran, Surah Al-Waaqia 56:77
إِنَّهُۥ لَقُرْءَانٌۭ كَرِيمٌۭ ﴿٧٧﴾
Indeed, it is a noble Qur'an
Arabic calls something noble or generous because of the good that comes through it.
Sunan an-Nasa'i 2106
Grading to be checked... أتاكم رمضان شهر مبارك فرض الله عز وجل عليكم صيامه ...
"Ramadan has come to you, a blessed month; Allah has made its fasting obligatory on you."
The Prophet ﷺ announced Ramadan to his Companions as good news.
Where the ruling is recorded
- Radd al-Muhtar (Ibn Abidin), Kitab al-Salah, chapter on the two Eids. Congratulating one another on blessed occasions such as Eid is not disliked.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.