Document and Entity Information Document - USD ($) $ in Billions	12 Months Ended
	Jan. 31, 2020	Mar. 23, 2020	Jul. 31, 2019
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jan. 31, 2020
Document Transition Report	false
Entity File Number	001-38240
Entity Registrant Name	MONGODB, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1463205
Entity Address, Address Line One	1633 Broadway
Entity Address, Address Line Two	38th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10019
City Area Code	646
Local Phone Number	727-4092
Title of 12(b) Security	Class A Common Stock, par value $0.001 per share
Trading Symbol	MDB
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 6.7
Entity Central Index Key	0001441816
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Current Fiscal Year End Date	--01-31
Class A Common Stock
Entity Common Stock, Shares Outstanding		48,962,130
Class B Common Stock
Entity Common Stock, Shares Outstanding		8,604,123