You can say “Eid Mubarak” from the start of Eid day, and it’s also fine (and common now) to say it a bit earlier in some contexts.

Short answer

Most scholars and traditional sources say the main time to say “Eid Mubarak” is:

  • From Fajr (dawn) on the day of Eid
  • Especially after the Eid prayer, as people meet and congratulate one another
  • Throughout the whole day of Eid, and even during the following days of celebration in many cultures

Saying it the night before (after the moon is confirmed and Eid is announced) is also widely practiced and considered okay by many, because the intention is to spread joy and good feelings.

Mini breakdown

1. The “safest” time

If you want to stick closely to classical opinions:

  • Start from Fajr on the day of Eid.
  • Say it after Eid salah when you meet people in the masjid or outside.
  • Continue using it the rest of the day when messaging, calling, or visiting others.

This timing clearly avoids any scholarly disagreement.

2. Saying it the night before

In real life today:

  • Many people start saying “Eid Mubarak” as soon as:
    • The moon is sighted / announcement is made
    • Work or school breaks start for Eid
  • Newer generations often treat it like New Year: once Eid is officially “coming in,” they begin sending greetings at night or at midnight.

Most contemporary teachers and writers consider this permissible , because:

  • The purpose is to show joy, love, and unity.
  • There’s a general principle that customs which spread kindness and don’t break a rule are allowed.

If you worry about being “too early,” you can add something like:
“Eid is tomorrow inshaAllah, just wanted to wish you an early Eid Mubarak!”

3. How long can you keep saying it?

In practice, people say “Eid Mubarak”:

  • All day on Eid itself.
  • Often the next day or two, especially if they didn’t see someone on the main day.
  • For Eid al-Adha, some greet through the days of Tashriq (the following days of ritual and celebration).

So, if you meet a friend two days later and it’s still in the Eid period, it’s totally fine to greet them with “Eid Mubarak” then.

A simple rule of thumb

If you want an easy guideline you can follow every year:

  1. Once Eid is officially announced , it’s okay to wish close friends and family “Eid Mubarak,” especially by message.
  2. From Fajr of Eid day, you can say it freely to everyone, and especially after Eid prayer.
  3. You can keep using it for the rest of the day and, if needed, the next couple of days when you first see someone.

This way you’re both respectful of tradition and relaxed with modern practice.

TL;DR

  • Best time: From Fajr on Eid day, especially after the Eid prayer.
  • Also okay in practice: After Eid is announced the night before, especially in messages or early greetings.
  • Still fine: Rest of Eid day and, if needed, the next few days when you first meet people.