Is Nifty 50 + Nifty Next 50 + a midcap fund a good SIP combination to build a corpus?

Yes — that structure is a textbook core-and-satellite portfolio. A Nifty 50 tracker gives you India's largest companies at rock-bottom cost, Nifty Next 50 adds the growth tier just below it (with zero stock overlap — the two indices hold different companies by construction), and a midcap fund brings the higher-growth, higher-volatility segment. Some investors add a multi-asset fund as a fourth leg so debt and gold cushion the equity drawdowns.

Two things decide whether the combo actually works. First, cost and tracking: for the index legs, expense ratio and tracking error are the whole game — the cheapest clean tracker usually wins. Second, overlap discipline: if you also hold a flexi cap or broad-market fund elsewhere, you may already own much of this; and an active midcap fund plus a Midcap 150 tracker would double the same exposure. Four SIPs is plenty — more funds usually adds paperwork, not diversification.

The cheapest large-cap index funds (Nifty 50 and Next 50 trackers) in our data are below, ranked by expense ratio. This is research, not investment advice.