What is a SIP, really?

Say you have a ₹5,000 monthly SIP dated the 5th. On the 5th, four things happen in order:

1. Your bank honours the mandate and ₹5,000 leaves your account.
2. The fund receives it and applies that day's Net Asset Value — the per-unit price.
3. You are allotted ₹5,000 ÷ NAV units. At an NAV of ₹250, that is 20 units. At ₹200, it is 25.
4. Those units are added to your folio. Nothing else about your holding changes.

Notice what is not happening. You are not buying "a SIP". There is no separate SIP product, no SIP interest rate, no maturity date. You own units in a mutual fund, exactly as you would if you had bought them in one go. The SIP is only the delivery mechanism.

This matters because it settles a lot of confused questions at once. "Which SIP should I buy?" is really "which fund should I buy?". "Is my SIP safe?" is really "how volatile is this fund?". And "my SIP is down" means the fund's NAV has fallen — the SIP itself cannot go up or down.

Because you invest a fixed rupee amount rather than buying a fixed number of units, you automatically buy more units when the price is low and fewer when it is high. Your average cost per unit therefore ends up below the average price over the period.

Here is that happening with four instalments of ₹5,000:

The average price across those four dates is ₹215. Your average cost is ₹207.79 — lower, without any skill or timing. That is real, and it is arithmetic rather than opinion.

But be clear about the limits. Averaging does not guarantee a profit: end at an NAV of ₹150 and you are down regardless. And in a market that only rises, averaging actively costs you, because every later instalment buys at a higher price than the first. Averaging is a way of removing the need to time your entry. It is not a return enhancer, and it is sold as one far too often.

First, and by a wide margin: it makes investing automatic. The largest single determinant of how much money you end up with is how much you invested and for how long. A standing instruction removes the monthly decision, and removing the decision is what stops the gap between "I should invest" and actually investing.

Second: it matches how income arrives. Most people receive money monthly, so investing monthly needs no accumulation phase where the cash sits in a savings account losing to inflation.

Notice that neither reason is "SIPs produce higher returns". They do not. For the same total money over the same period at a steady positive rate, a lump sum on day one beats a SIP — you can verify that in the comparison calculator. The SIP's advantage is behavioural and practical, and that is more than enough.

• Regular SIP — fixed amount, fixed date. The default, and right for most people.
• Step-up or top-up SIP — the amount rises automatically each year. The single most useful variant; see step-up SIP explained.
• Perpetual SIP — no end date, runs until you stop it. Mostly an administrative convenience, and it removes an accidental lapse when a fixed term expires.
• Flexible SIP — you vary the amount. In practice this reintroduces the monthly decision the SIP existed to remove.
• Trigger SIP — invests more when the market falls by some threshold. This is market timing with extra steps, and it needs you to have idle cash waiting, which has its own cost.