New Delhi, Oct. 14 -- The first piece of advice almost every new investor receives is the same: start a systematic investment plan (SIP), pick a date and let it run. It is sound advice. But it also quietly assumes something many people do not have: a paycheque that arrives on the same day every month.

Freelancers, consultants, traders and small business owners all deal with income that does not follow a fixed schedule. Some months are busy, others are lean, and a single large invoice can arrive a quarter late. For them, the standard monthly-SIP playbook is not just difficult to follow; it is built on a foundation they do not have.

So what should investing look like when income itself is irregular?

The mistake is to treat the SIP as the...