Guru Nanak was born on 15 April 1469, now celebrated as Guru Nanak Gurpurab, at Rai Bhoi Ki Talva??i, now called Nankana Sahib, near Lahore, in present day Pakistan. Today, his birthplace is marked by Gurdwara Janam Asthan. His parents were Kalyan Chand Das Bedi, popularly shortened to Mehta Kalu, and Mata Tripta. His father was a patwari (accountant) for crop revenue in the village of Talwandi, employed by a Muslim landlord of that area, Rai Bular Bhatti.

He had one sister, Bibi Nanaki, who was five years older than him and became a spiritual figure in her own right. In 1475 she married Jai Ram and went to his town of Sultanpur, where he was the steward (modi) to Daulat Khan Lodi, the eventual governor of Lahore during the Afghan Lodhi dynasty. Nanak was attached to his older sister, and, in traditional Indian fashion, he followed her to Sultanpur to live with her and her husband. Nanak also found work with Daulat Khan, when he was around 16 years old. This was a formative time for Nanak, as the Puratan (traditional) Janam Sakhi suggests, and in his numerous allusions to governmental structure in his hymns, most likely gained at this time.

Commentaries on his life give details of his blossoming awareness from a young age. At the age of five, Nanak is said to have voiced interest in divine subjects. At age seven, his father enrolled him at the village school as was the custom. Notable lore recounts that as a child Nanak astonished his teacher by describing the implicit symbolism of the first letter of the alphabet, which is an almost straight stroke in Persian or Arabic, resembling the mathematical version of one, as denoting the unity or oneness of God.Other childhood accounts refer to strange and miraculous events about Nanak, such as one witnessed by Rai Bular, in which the sleeping childs head was shaded from the harsh sunlight, in one account, by the stationary shadow of a tree or, in another, by a poisonous cobra.