New Delhi, June 22 -- A market crash is usually bad news for investors, as portfolio values fall and returns turn negative. But for investors running a systematic investment plan (SIP), a correction can create an often-overlooked opportunity.

Because SIPs invest a fixed amount at regular intervals, falling markets allow investors to buy more units of mutual funds. If markets recover later, those additional units can lift long-term returns and improve XIRR, the standard measure of SIP performance.

This is one reason why many financial advisers stress that investors should continue their SIPs during market downturns rather than stop them.

Unlike lump-sum investing, SIPs involve multiple investments at different NAVs over time. Since cash...