Document and Entity Information	Total
Prospectus:
Document Type	485BPOS
Document Period End Date	Oct. 31, 2022
Entity Registrant Name	MFS® SERIES TRUST IX
Entity Central Index Key	0000063075
Entity Inv Company Type	N-1A
Amendment Flag	false
Document Creation Date	Feb. 27, 2023
Document Effective Date	Feb. 28, 2023
Prospectus Date	Feb. 28, 2023
MFS Inflation-Adjusted Bond Fund \| R6
Prospectus:
Trading Symbol	MIAKX
MFS Inflation-Adjusted Bond Fund \| A
Prospectus:
Trading Symbol	MIAAX
MFS Inflation-Adjusted Bond Fund \| R4
Prospectus:
Trading Symbol	MIAJX
MFS Inflation-Adjusted Bond Fund \| B
Prospectus:
Trading Symbol	MIABX
MFS Inflation-Adjusted Bond Fund \| C
Prospectus:
Trading Symbol	MIACX
MFS Inflation-Adjusted Bond Fund \| I
Prospectus:
Trading Symbol	MIAIX
MFS Inflation-Adjusted Bond Fund \| R1
Prospectus:
Trading Symbol	MIALX
MFS Inflation-Adjusted Bond Fund \| R2
Prospectus:
Trading Symbol	MIATX
MFS Inflation-Adjusted Bond Fund \| R3
Prospectus:
Trading Symbol	MIAHX

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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