A SIP, or systematic investment plan, is the most common way Indians invest in mutual funds. Instead of putting in a large lump sum, you invest a fixed amount, say ₹5,000, on a fixed date every month. The money is taken from your bank account automatically and used to buy units of the fund you chose at that day's price. This guide explains how a SIP works, what "rupee cost averaging" really means, how compounding adds up, and where SIPs fall short.
How a SIP works, step by step
- You choose a mutual fund, an amount and a date (for example ₹5,000 on the 5th of every month).
- You sign a bank mandate so the amount can be debited automatically.
- On each date, the amount is invested at that day's NAV (net asset value, the price of one unit). You receive units, including fractions of a unit.
- The units add up in your folio. Their value goes up and down with the fund's NAV.
- You can pause, change or stop the SIP, and redeem units whenever you need (subject to any exit load or lock-in).
SIPs work with mutual funds of every kind: equity, debt, hybrid, index funds and gold funds. Some brokers also let you buy ETF units on a schedule, though in whole units only (see ETF vs mutual fund).
Rupee cost averaging, with numbers
Because you invest the same rupee amount each time, you automatically buy more units when the NAV is low and fewer when it is high. Here is a four-month example with ₹10,000 a month:
| Month | NAV (₹) | Amount (₹) | Units bought |
|---|---|---|---|
| 1 | 100 | 10,000 | 100 |
| 2 | 80 | 10,000 | 125 |
| 3 | 125 | 10,000 | 80 |
| 4 | 100 | 10,000 | 100 |
| Total | 40,000 | 405 |
Your average cost per unit is ₹40,000 ÷ 405 = ₹98.77, while the average NAV over the four months was ₹101.25. Buying more units in the cheap month pulled your cost down. At the end, with the NAV back at ₹100, your 405 units are worth ₹40,500: a small gain even though the NAV ended where it started.
Rupee cost averaging does not guarantee a profit. If the NAV falls and stays low, you still lose money. It only means you never put all your money in at a single high point.
Compounding over long periods
The bigger effect of a SIP is time. Gains are reinvested inside the fund and themselves earn returns. The usual formula for the value of a monthly SIP is:
Future value = P × [((1 + r)ⁿ − 1) ÷ r] × (1 + r)
Here P is the monthly amount, r the monthly return and n the number of months; (1 + r)ⁿ means (1 + r) multiplied by itself n times. Example: ₹10,000 a month for 15 years (180 months), assuming 12% a year (taken as 1% a month for simplicity):
- Total invested: ₹18,00,000.
- Estimated value: about ₹50 lakh.
- Gain: about ₹32 lakh, most of it earned in the later years.
Stretch the same SIP to 25 years and the estimate rises to roughly ₹1.9 crore on ₹30 lakh invested. That is the power of compounding, but the assumed 12% is only an assumption. Real returns vary year to year, can be negative for long stretches, and depend heavily on the fund and the market. You can try your own numbers on the SIP calculator.
SIPs and market mood
The hardest part of a SIP is not starting it but continuing it when markets fall. The market mood score below tracks how fearful or greedy Indian investors are:
When the reading is fear, many investors are tempted to stop their SIPs, yet those are the months when a fixed amount buys the most units. When it reads greed, people often raise their SIPs just as prices are high. The market mood guide explains how the score is built. A SIP works best when it runs through both.
SIP or lump sum?
- A lump sum invested at once has more time in the market. If markets rise steadily, it usually ends higher than spreading the same money over months.
- A SIP spreads the timing risk. If markets fall soon after you start, it ends higher than a lump sum.
- For most salaried people the question does not arise: income arrives monthly, so investing monthly is natural.
Some investors with a lump sum use a systematic transfer plan (STP): they park it in a debt or liquid fund and move a fixed amount into an equity fund each month.
How to measure a SIP's return: XIRR
A SIP has many small investments made on different dates, so a simple "gain divided by amount invested" is misleading: money invested last month has had no time to grow, while money invested five years ago has had a lot. The standard measure is XIRR (extended internal rate of return). It works out the single yearly return that would turn each instalment, from its own date, into today's value.
Example: you invested ₹10,000 a month for 3 years (₹3,60,000 in total) and the units are now worth ₹4,30,000. The simple gain is about 19%, but that is not 19% a year, nor 19% over three years for all the money. The XIRR here works out to about 12% a year, because the average rupee was invested for only about half the period. Fund statements and most spreadsheet programs calculate XIRR for you. Compare it with the fund's benchmark index over the same dates, not with a fixed deposit rate quoted for a single lump sum.
Useful SIP features
- Step-up (top-up) SIP: increases the SIP by a fixed amount or percentage every year, often in line with salary rises.
- Pause: many fund houses let you pause a SIP for a few months without cancelling it.
- Direct plans: investing in a direct plan rather than a regular plan avoids distributor commission and lowers the expense ratio.
- Lock-in funds: in tax-saving funds (ELSS), each SIP instalment has its own lock-in period, counted from its own date. Check current rules.
Common mistakes
- Stopping in a fall. This turns temporary losses into permanent ones and misses the cheap months.
- Too many SIPs in similar funds. Five large-cap funds hold mostly the same shares; it adds paperwork, not safety.
- Judging a SIP after one year. Equity SIPs are built for long periods; one year says very little.
- Using a SIP for money needed soon. Money needed within a couple of years is usually better kept out of equity funds.
- Believing a SIP is a product. It is a way of investing; the risk comes from the fund you choose.