SIP Explained: Worked NAV Example, XIRR Returns and Tax

What a SIP Actually Is

A Systematic Investment Plan (SIP) is an instruction you give a mutual fund, or a platform such as a broker app, Groww, Zerodha Coin or the AMC website, to invest a fixed rupee amount into a chosen scheme on a fixed date every period. Most SIPs are monthly, but daily, weekly and quarterly options exist. On each due date the amount is auto debited from your bank through an NACH mandate, and the fund allots you units at that day's Net Asset Value (NAV). A SIP is therefore not a product you buy. It is a disciplined way of buying one product, the underlying mutual fund, again and again.

The unit count is what compounds your wealth, not the rupee amount. If a Nifty 50 index fund has an NAV of Rs 95.20 on the day your Rs 10,000 hits, you receive 105.0420 units. Next month the same Rs 10,000 might buy 113.1222 units because the NAV slipped to Rs 88.40. Your money bought more of the fund precisely when it was cheaper. Over years these fractional units add up, and the final value is simply your total units multiplied by the NAV on the day you sell.

SIPs are regulated under the SEBI mutual fund framework. There is no lock in on an open ended equity or debt fund SIP, so you can pause, stop, increase or redeem at will. The one common exception is an ELSS tax saver fund, where each instalment is locked for three years from its own date.

A Real Worked SIP Example With NAV History and XIRR

Here is the part most SIP explainers skip. Numbers below are illustrative and use realistic NAV levels for a large Nifty 50 index fund through one rising year. They are not a promise of returns. Say you invest Rs 10,000 on the 1st of every month for twelve months, from 1 January 2025 to 1 December 2025, into the same Nifty 50 index fund. Each instalment buys units at that month's NAV. The table tracks exactly what happens.

After twelve instalments you have invested Rs 1,20,000 and you hold 1,232.99 units. Your average cost is Rs 1,20,000 divided by 1,232.99, which is about Rs 97.32 per unit. Notice that the average NAV across the twelve months was Rs 97.69, yet your average cost came out lower at Rs 97.32. That small gap is rupee cost averaging working in your favour, because the SIP automatically bought slightly more units in the cheap months.

Now value the holding. Suppose on the valuation date of 1 January 2026 the NAV is Rs 110.40. Your 1,232.99 units are worth 1,232.99 times Rs 110.40, which is Rs 1,36,121.76. On Rs 1,20,000 invested, the gain is Rs 16,121.76. As a flat number that is a 13.43 percent absolute return. But that figure is misleading, because your December instalment was invested for only one month while your January instalment was invested for a full year.

Why XIRR Is the Only Honest SIP Return Number

A simple return percentage assumes all your money went in on day one. With a SIP that is false. The correct measure is XIRR, the extended internal rate of return, which is the single annualised rate at which all your dated outflows and the final inflow balance to zero. In a spreadsheet it is the XIRR function fed with each instalment date as a negative cash flow and the redemption value as a positive cash flow on the valuation date.

For the example above, the twelve negative cash flows of Rs 10,000 and the single positive cash flow of Rs 1,36,121.76 on 1 January 2026 solve to an XIRR of about 25.6 percent. That is far higher than the 13.43 percent absolute figure, and that is correct, because most of your rupees were only invested for a few months. XIRR annualises that short exposure. The lesson for traders is blunt. Never compare a SIP and a lump sum using absolute return. Compare them on XIRR, which puts both on the same annual footing.

Rupee Cost Averaging, and Where It Stops Helping

Rupee cost averaging is the structural advantage of a SIP. Because the rupee amount is fixed and the NAV moves, you buy more units when the fund is cheap and fewer when it is expensive. Over a choppy or falling stretch this drags your average cost below the simple average price, which is exactly what happened above. It removes the need to time the market, which most investors and even most professionals do badly.

Be honest about the limit, though. Rupee cost averaging helps most in sideways or volatile markets. In a market that rises in a near straight line, a lump sum invested at the start beats a SIP, because the SIP keeps buying at higher and higher NAVs. Indian equity markets have historically trended up over long periods, which is one reason a one time lump sum, when you actually have the cash, often outperforms a SIP of the same total over a long bull run. The SIP still wins on discipline, cash flow fit and emotional safety, which is usually why salaried investors choose it.

• SIP shines when you earn monthly and cannot deploy a large sum at once.
• SIP shines in volatile or falling markets, where averaging pulls your cost down.
• Lump sum can beat SIP in a steady bull run, since every later instalment buys dearer.
• A step up SIP, where you raise the amount yearly with your salary, usually beats a flat SIP over a decade.

How SIP Tax Works in India Today

Tax on a SIP is calculated per instalment, not on the SIP as a whole, and units are sold on a first in, first out basis. Each monthly purchase has its own purchase date, so when you redeem, the oldest units leave first and the holding period is measured from that specific instalment. This matters because in any single redemption some units may be long term and some short term.

For equity oriented funds, the rules effective after the July 2024 budget are clear. Units held one year or less are short term, taxed at a flat STCG of 20 percent. Units held more than one year are long term, and LTCG is 12.5 percent on gains above Rs 1.25 lakh in a financial year, with no indexation. The earlier 15 percent STCG and 10 percent above Rs 1 lakh LTCG no longer apply. A 4 percent health and education cess sits on top of the tax. For debt funds bought on or after 1 April 2023, all gains are added to your income and taxed at your slab rate regardless of holding period, so the old three year and indexation route is gone for new debt money.

SIP Versus Trading a Nifty Position

A SIP and an F&O trade are different animals, and confusing them is a common beginner error on this site's calculators. A SIP holds units in a fund and pays capital gains tax. An F&O trade in Nifty or Bank Nifty is treated as business income, taxed at your slab rate, with no capital gains rate. Suppose instead of a SIP you buy one lot of Nifty 50, lot size 65, by buying a 23,000 strike call at a premium of Rs 150, and exit at Rs 230. Your gross profit is the move of Rs 80 times 75, which is Rs 6,000, before brokerage, exchange fees, STT and GST.

On that options trade, STT applies at 0.1 percent on the sell side premium, brokerage plus GST and exchange charges eat into the rest, and the net profit is added to your income as business income. Contrast that with the SIP, where you do nothing for a year, pay no STT on purchases, and face a clean 12.5 percent LTCG only on gains above Rs 1.25 lakh once you redeem after a year. The SIP is a slow wealth machine. The Nifty option is a fast, leveraged, expiry bound bet.

• SIP: no leverage, no expiry, capital gains tax, designed to be held for years.
• Nifty or Bank Nifty F&O: leverage, weekly or monthly expiry, business income tax, designed to be held for days or hours.
• A Rs 10,000 monthly SIP and a one lot Nifty option are not comparable risk, so size them separately in your plan.

Choosing and Setting Up a SIP

Pick the scheme before you pick the amount. For a first SIP, a low cost Nifty 50 or Sensex index fund is the simplest honest choice, because it tracks the broad market, has a low expense ratio, and removes the risk of a star fund manager underperforming. Active large cap, flexi cap and mid cap funds can be added later once you understand the extra cost and the manager risk. Always choose the direct plan, not the regular plan, since direct plans skip the distributor commission and quietly add roughly half a percent to one percent a year to your returns.

Then complete a one time KYC, link your bank, set up the NACH auto debit mandate, and select the SIP date a day or two after your salary credit so the account is funded. Start with an amount you will not feel pressure to stop, even in a bad month, because the single most damaging SIP mistake is stopping during a fall, which is exactly when the averaging is working hardest for you. Increase the amount yearly through a step up SIP rather than starting too big.

• Prefer a low cost index fund and the direct plan for your first SIP.
• Set the SIP date just after payday so the auto debit never bounces.
• Keep the amount sustainable so you never stop during a market fall.
• Use a step up SIP to raise the amount with your income each year.
• Review once or twice a year against the benchmark, not every week.

Common SIP Mistakes That Quietly Cost You

The biggest mistake is psychological, not financial. Investors stop the SIP when the market falls, which cancels the one feature, cheap buying, that makes SIPs work. The second mistake is chasing last year's top fund, since today's chart topper is often tomorrow's laggard, and switching repeatedly triggers exit loads and tax. The third is holding too many SIPs in funds that all own the same large cap stocks, which feels like diversification but is not.

There are quieter leaks too. A regular plan donates part of your return to a distributor every year for decades. Ignoring the expense ratio means a high cost active fund must beat the index by its own fee just to draw level. And redeeming without checking which units are still short term can trigger 20 percent STCG that a few weeks of patience would have turned into 12.5 percent LTCG.

• Stopping the SIP in a downturn, the single costliest error.
• Chasing last year's best fund and churning through exit loads and tax.
• Owning many funds that secretly hold the same large caps.
• Picking a regular plan when a cheaper direct plan exists.
• Redeeming short term units and paying 20 percent STCG needlessly.

Reviewing Your SIP Without Overtrading It

A SIP is meant to be boring, but it still needs a check up. Once or twice a year, compare your equity fund against its benchmark, the Nifty 50 TRI for a large cap fund or the relevant index otherwise. A fund that lags its benchmark for three or more years, after fees, is a reason to consider switching. A fund that lags for one quarter is not.

Look at three things during a review. First, XIRR on your consolidated statement, which is the real annualised return on your actual instalments. Second, the expense ratio, since a creeping fee silently erodes returns. Third, whether the fund still matches your goal and risk. Rebalance between equity and debt only at the band you set, not on a hunch.

Sources and Further Reading

For authoritative data and current rules, refer to AMFI for NAV history and scheme data, Income Tax Department for capital gains rates, and SEBI Investor Education for mutual fund regulation. The NAV figures, returns and XIRR in this guide are illustrative and not a forecast. Always confirm current rates, expense ratios and contract specifications on the official source before you invest.

Sources and Further Reading

For authoritative data and further reading on this topic, refer to AMFI, Income Tax Department and SEBI Investor Education. Always confirm current rules, rates and contract specifications on the official source before you trade.