A SIP automates investing. You commit a set amount, say Rs 5,000 a month, and it is debited from your bank account automatically on a fixed date and used to buy units of the mutual fund you chose. You do not time the market, place an order, or make a decision each month. That is the entire point.
How a SIP actually works
On your chosen date, the money leaves your account and buys units at that day's NAV, the fund's per-unit price. If the NAV is Rs 50, your Rs 5,000 buys 100 units. If markets have fallen and the NAV is Rs 40, the same Rs 5,000 buys 125 units. Your unit count grows every month, and what those units are worth depends on where the fund's holdings are priced when you eventually sell.
There is no lock-in on an open-ended equity fund, with one exception: an ELSS tax-saving fund locks each instalment for three years from the date it was invested.
Rupee cost averaging, with real numbers
This is the mechanism people mean when they say SIPs reduce risk, and it is worth seeing rather than taking on trust.
Suppose you invest Rs 6,000 a month for three months and the NAV moves Rs 100, then Rs 75, then Rs 120. You buy 60 units, then 80 units, then 50 units: 190 units for Rs 18,000, an average cost of about Rs 94.74 per unit. But the simple average of the three prices is Rs 98.33. You paid less than the average price, without predicting anything, purely because a fixed rupee amount automatically buys more units when prices are low. That is rupee cost averaging.
It does not protect you from a market that falls and stays down. It protects you from the far more common problem of investing everything on one unlucky day.
What a SIP can realistically grow to
A Rs 5,000 monthly SIP, if it earned 12% a year, would be worth roughly Rs 11.6 lakh after 10 years against Rs 6 lakh invested. Stretch it to 20 years and it reaches about Rs 50 lakh against Rs 12 lakh invested. Doubling the time did not double the outcome. It more than quadrupled it, because compound interest does most of its work late.
Treat 12% as an assumption, not a promise. Equity returns are not smooth or guaranteed, and a decade that averages 12% will still contain years of double-digit losses. Our SIP calculator lets you test more conservative rates, which is a healthier way to plan.
SIP or lump sum?
If the money arrives monthly from a salary, the question does not really exist. A SIP is simply how you invest income as it comes. The comparison only matters when you are holding a lump sum, from a bonus or a maturity, and wondering whether to deploy it at once or spread it out.
Mathematically, investing a lump sum immediately wins more often than not, because markets rise over most long periods and money invested earlier compounds longer. Behaviourally, staggering it hurts far less when the market drops the following week. Our guide on SIP vs lump sum works through both cases.
How to start one
You need a PAN, a bank account and completed KYC. From there you can start directly on a fund house's own website, through a broker or investment app, or via a registered mutual fund distributor. You choose the fund, the amount, the date and the frequency, and set up a mandate that lets the fund debit your account each month.
Start with an amount you will not be tempted to stop during a bad quarter. Rs 1,000 sustained for a decade beats Rs 10,000 abandoned after eight months.
Where people go wrong
The most expensive mistake is stopping a SIP when markets fall. Those are precisely the instalments that buy the most units, and cancelling them converts a temporary decline into a permanent loss of the recovery.
The second is chasing last year's best-performing fund each year, which reliably buys high. The third is running a SIP with no goal and no horizon, so there is nothing to hold on to when the value dips. Decide upfront what the money is for and when you need it, then let the automation do its job.