Narrated Abu Bakr RA,

The Prophet Sallallahu alaihi wasallam said,

"The division of time has turned to its original form which was current when Allah created the Heavens and the Earths. The year is of twelve months, out of which four months are sacred: Three are in succession Dhul-Qa' da, Dhul-Hijja and Muharram, and (the fourth is) Rajab of (the tribe of) Mudar which comes between Jumadi-ath-Thaniyah and Sha ban."

Sahih Al-Bukhari, book of Beginning of Creation

Rajab has started last Friday

Shaban starts August ~ 2nd

Ramadan starts September ~ 1st.