The German international has not yet undergone a medical and is still with the National Team as they prepare for their Nations League matches against Spain and Switzerland.
Chelsea who have been in talks with Bayer for much of the summer finally had a breakthrough in negotiations on Wednesday.
The fee surpasses the previous club record deal of £71.6m paid for goalkeeper Keeps Arrizabalaga from Athletic Bilbao in 2018.
Havertz will become Frank Lampard’s seventh signing.