What a SIP actually does
A systematic investment plan invests a fixed amount at a fixed interval, usually monthly. Its value is not primarily mathematical — it is that it removes the decision. Nothing to time, nothing to judge, no market news to react to.
That matters more than it sounds. The largest destroyer of long-term returns is not poor fund selection; it is stopping during downturns and restarting after recoveries. An automated instalment is the simplest defence against your own reactions.
The step-up, which most calculators ignore
A flat instalment held for twenty years quietly shrinks in real terms. Your income rises; your investment does not.
Try it above. At 12% over 15 years, $500 a month reaches around $250,000. With a 10% annual step-up, the same starting instalment reaches substantially more — because each year's increase compounds for every remaining year.
Practically, a step-up matched to your annual raise costs nothing in lifestyle terms: you never see the money as spendable income, so it does not feel like a sacrifice. It is the single easiest improvement available to most investors.
Rupee cost averaging, honestly
SIPs are frequently sold on cost averaging: fixed instalments buy more units when prices are low and fewer when high, averaging your purchase price.
This is true and oversold. Averaging reduces the variance of your entry price; it does not reliably raise expected returns. Studies generally find that investing a lump sum immediately beats staggering it about two thirds of the time, because markets rise more often than they fall.
The real benefits are consistency and automation. Those are worth a great deal. The averaging is a side effect.
Being realistic about returns
A 12% assumption is common in Indian SIP illustrations and is roughly in line with long-run Indian equity index returns. It is not a promise, and it will not arrive smoothly.
Indian markets have fallen more than 40% on multiple occasions. A portfolio averaging 12% over fifteen years might return 35% one year and lose 25% the next. The average is an outcome, not a schedule.
Run the calculator at 9% and 15% as well as 12%. If your plan only works at the optimistic figure, it is not a plan.
What matters more than the instalment size
Costs. A direct plan rather than a regular plan typically saves 0.5–1% a year in expense ratio. Over twenty years that difference alone runs into a large sum, and it is guaranteed rather than hoped for.
Duration. Compare 15 years against 20 in the calculator. Five extra years usually adds more than raising the instalment by half, because those years operate on the largest balance.
Not stopping. Everything above is void if contributions halt during a fall. That is when units are cheapest and when the arithmetic works hardest in your favour.
Frequently asked questions
What is a step-up SIP?
A SIP where the monthly instalment increases by a set percentage each year, usually matched to your annual raise. Because each increase compounds for all remaining years, a 10% annual step-up produces substantially more than a flat instalment over long periods.
What return should I assume for a SIP?
Around 12% is common in Indian illustrations and roughly matches long-run equity index returns, but it is an average outcome rather than a schedule - Indian markets have fallen over 40% on multiple occasions. Run 9% and 15% as well, and plan against the lower figure.
Is SIP better than a lump sum?
On expectation, investing a lump sum immediately wins about two thirds of the time, because markets rise more often than they fall. SIPs win on behaviour: they remove timing decisions and prevent the scenario where you invest everything just before a fall and then sell.
Should I stop my SIP when markets fall?
No. That is when your instalment buys the most units. Stopping during falls and restarting after recoveries is the most common and most costly mistake in long-term investing.