Primary Capital Market Transactions and Index Funds

Abstract We document how mechanical buying by CRSP-index-tracking funds 5 days post-IPO affects stock returns and IPO deal structure. Using a difference-in-differences design, we show that expected indexer demand causes Fast-Track IPOs to outperform their non-Fast-Track counterparts by over five percentage points, peaking at the index inclusion date and reverting significantly within 3 weeks. Anticipated CRSP index inclusion also affects IPO terms, with Fast-Track IPOs raising 6% more capital than their non-Fast-Track counterparts. Our findings support a proposed index rule change to eliminate a $5.8 billion “shadow tax” paid to intermediaries by index fund investors and firms raising capital through IPOs. (JEL G12, G14) Received: 14 March 2025; Editorial decision: September 9, 2025Editor: Joel PeressAuthors have furnished an Internet Appendix, which is available on the Oxford University Press Web site next to the link to the final published paper online.