The tax loss harvest partner I use for VTSAX is VFIAX. Like others have suggested here, it is the Vanguard 500 index fund, and commonly referenced as a VTSAX TLH partner. The ETF version of VFIAX is VOO. Don't forget to consider other accounts that you may be purchasing similar funds in, such as retirement accounts and possibly even kids accounts. I've read differing things about UTMA accounts and whether their transactions trigger wash sale rules...