Document and Entity Information - shares	3 Months Ended
	Apr. 30, 2018	Jun. 04, 2018
Document Information [Abstract]
Entity Registrant Name	MongoDB, Inc.
Entity Central Index Key	0001441816
Current Fiscal Year End Date	--01-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Apr. 30, 2018
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Class A Common Stock
Entity Common Stock, Shares Outstanding		24,766,963
Class B Common Stock
Entity Common Stock, Shares Outstanding		25,864,505