Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Jun. 30, 2025	Aug. 25, 2025	Dec. 31, 2024
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jun. 30, 2025
Current Fiscal Year End Date	--06-30
Document Transition Report	false
Entity File Number	814-00659
Entity Registrant Name	PROSPECT CAPITAL CORP
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	43-2048643
Entity Address, Address Line One	10 East 40th Street
Entity Address, Address Line Two	42nd Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10016
City Area Code	212
Local Phone Number	448-0702
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 1,349
Entity Common Stock, Shares Outstanding		462,343,452
Documents Incorporated by Reference	Documents Incorporated by Reference Portions of the Registrant’s definitive Proxy Statement relating to the 2025 Annual Meeting of Stockholders, to be filed with the Securities and Exchange Commission, are incorporated by reference in Part III of this Annual Report on Form 10-K to the extent described therein.
Entity Central Index Key	0001287032
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	PSEC
Security Exchange Name	NASDAQ
5.35% Series A Fixed Rate Cumulative Perpetual Preferred Stock, par value $0.001
Document Information [Line Items]
Title of 12(b) Security	5.35% Series A Fixed Rate Cumulative Perpetual Preferred Stock, par value $0.001
Trading Symbol	PSEC PRA
Security Exchange Name	NYSE