Short answer
As long as it takes to say one sentence. You become Muslim the moment you sincerely say the shahada, with no waiting period, course or test. Learning the religion is a lifelong journey taken step by step, starting with the five daily prayers.
Islam is established by belief in the heart and the shahada on the tongue. No waiting period, class, witness or certificate is a condition, and once a person believes, delaying the shahada is not allowed. The duties of Islam begin from that moment and are learned gradually, starting with prayer.
The four schools agree on this.
Explanation
Some people expect a process like baptism classes or a long conversion course. Islam has nothing of the kind. If you believe there is no god but Allah and that Muhammad ﷺ is His messenger, say the shahada and you are Muslim. The four schools agree that no ceremony, waiting time or approval is required.
Learning is a different matter, and Islam expects it to be gradual. When the Prophet ﷺ sent Muadh to Yemen, he told him to call people first to the shahada, then, once they accepted, to teach them the five prayers, and after that zakat. New Muslims are taught the same way.
- Day one: say the shahada, take a ghusl, and avoid pork and alcohol from now on.
- First weeks: learn wudu and how to pray. Start with what you can manage and build up to all five prayers.
- First months: learn Surah al-Fatiha and a few short surahs, the basics of halal food, and fast Ramadan when it comes.
- Over time: zakat when you have savings above the nisab, reading the Quran, and Hajj if you can afford it.
Some mosques offer a class before the shahada, and it is fine to read and ask questions while you are still deciding. But once you are convinced, do not wait until you feel you know enough or have fixed every habit: nobody does. See converting while still struggling with sins and the new Muslim guide.
The evidence
Quran, Surah Al-Baqara 2:185
شَهْرُ رَمَضَانَ ٱلَّذِىٓ أُنزِلَ فِيهِ ٱلْقُرْءَانُ هُدًۭى لِّلنَّاسِ وَبَيِّنَٰتٍۢ مِّنَ ٱلْهُدَىٰ وَٱلْفُرْقَانِ ۚ فَمَن شَهِدَ مِنكُمُ ٱلشَّهْرَ فَلْيَصُمْهُ ۖ وَمَن كَانَ مَرِيضًا أَوْ عَلَىٰ سَفَرٍۢ فَعِدَّةٌۭ مِّنْ أَيَّامٍ أُخَرَ ۗ يُرِيدُ ٱللَّهُ بِكُمُ ٱلْيُسْرَ وَلَا يُرِيدُ بِكُمُ ٱلْعُسْرَ وَلِتُكْمِلُوا۟ ٱلْعِدَّةَ وَلِتُكَبِّرُوا۟ ٱللَّهَ عَلَىٰ مَا هَدَىٰكُمْ وَلَعَلَّكُمْ تَشْكُرُونَ ﴿١٨٥﴾
The month of Ramadhan [is that] in which was revealed the Qur'an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you; and perhaps you will be grateful.
The religion is meant to be easy to take up and practise.
Quran, Surah An-Nisaa 4:136
يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ ءَامِنُوا۟ بِٱللَّهِ وَرَسُولِهِۦ وَٱلْكِتَٰبِ ٱلَّذِى نَزَّلَ عَلَىٰ رَسُولِهِۦ وَٱلْكِتَٰبِ ٱلَّذِىٓ أَنزَلَ مِن قَبْلُ ۚ وَمَن يَكْفُرْ بِٱللَّهِ وَمَلَٰٓئِكَتِهِۦ وَكُتُبِهِۦ وَرُسُلِهِۦ وَٱلْيَوْمِ ٱلْءَاخِرِ فَقَدْ ضَلَّ ضَلَٰلًۢا بَعِيدًا ﴿١٣٦﴾
O you who have believed, believe in Allah and His Messenger and the Book that He sent down upon His Messenger and the Scripture which He sent down before. And whoever disbelieves in Allah, His angels, His books, His messengers, and the Last Day has certainly gone far astray.
Faith is belief in Allah, His messenger and His revelation, which the shahada expresses.
Sahih al-Bukhari 1395
Sahih... ادعهم إلى شهادة أن لا إله إلا الله وأني رسول الله ...
"Invite them to bear witness that there is no god but Allah and that I am the messenger of Allah. If they accept that, teach them that Allah has made five prayers obligatory on them each day and night."
The Prophet ﷺ taught new Muslims step by step, starting with the shahada.
Where the ruling is recorded
- al-Fiqh al-Akbar, the section on the definition of iman. Faith is belief in the heart affirmed by the tongue.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Jihad, Bab al-Murtadd, discussion of how a person becomes Muslim. No witness or ceremony is a condition of entering Islam.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. 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.