Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2025	May 12, 2025
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Fiscal Year Focus	2025
Document Period End Date	Mar. 31, 2025
Document Fiscal Period Focus	Q1
Entity Central Index Key	0002013639
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-42380
Entity Registrant Name	FB Bancorp, Inc.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	99-1859402
Entity Address, Address Line One	353 Carondelet Street
Entity Address, City or Town	New Orleans
Entity Address, State or Province	LA
Entity Address, Postal Zip Code	70130
City Area Code	504
Local Phone Number	569-8640
Trading Symbol	FBLA
Title of 12(b) Security	Common
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		19,837,500
Amendment Flag	false