v3.25.1
Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType 497
Document Period End Date dei_DocumentPeriodEndDate Dec. 31, 2024
Registrant Name dei_EntityRegistrantName MFS VARIABLE INSURANCE TRUST
Entity Central Index Key dei_EntityCentralIndexKey 0000918571
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate May 05, 2025
Document Effective Date dei_DocumentEffectiveDate May 05, 2025
EntityInvCompanyType dei_EntityInvCompanyType N-1A
Prospectus Date rr_ProspectusDate Apr. 30, 2025
MFS Growth Series | Initial Class Shares  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol N/A
MFS Growth Series | Service Class Shares  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol N/A