v3.25.2
Cover
Jun. 13, 2025
Cover [Abstract]  
Document Type 8-K
Amendment Flag false
Document Period End Date Jun. 13, 2025
Entity File Number 814-01639
Entity Registrant Name New Mountain Guardian IV Income Fund, L.L.C.
Entity Central Index Key 0001976719
Entity Tax Identification Number 92-0964074
Entity Incorporation, State or Country Code DE
Entity Address, Address Line One 1633 Broadway
Entity Address, Address Line Two 48th Floor
Entity Address, City or Town New York
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10019
City Area Code 212
Local Phone Number 720-0300
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Entity Emerging Growth Company true
Elected Not To Use the Extended Transition Period false