SIP vs lump sum, and what a step-up SIP changes
Last updated 2026-10-05
A SIP puts a fixed amount in every month; a lump sum goes in all at once. They are often compared as if one must win. The numbers show something more useful: how much of the result comes from time and the assumed return rather than the monthly amount.
What a SIP projection assumes
The projection compounds each monthly instalment at the yearly return divided by 12, with each instalment invested at the start of its month. It is an estimate: real fund returns move around, so an assumed 12% a year is a planning input, not a promise. Taxes, exit loads and inflation are not applied, and fund expenses are assumed to be inside the return you enter.
The same SIP at different returns
Rs 10,000 a month for 20 years puts in Rs 24 lakh whatever happens. At an assumed 8% it grows to about Rs 59.3 lakh, at 10% about Rs 76.6 lakh, at 12% about Rs 99.9 lakh and at 15% about Rs 1.52 crore. The investment is identical; only the assumption moves, which is why running a low, middle and high rate is more honest than relying on one.
What a yearly step-up does
A step-up SIP raises the instalment by a set percentage each year, for example with salary. Rs 10,000 a month at 12% for 15 years is about Rs 50.5 lakh as a flat SIP. With a 10% yearly step-up it is about Rs 86.8 lakh, from Rs 38.1 lakh invested instead of Rs 18 lakh. Over 20 years the stepped version reaches about Rs 1.99 crore against Rs 99.9 lakh flat.
The extra comes from paying more, not from a better return, so a step-up only helps if you can actually afford the larger instalments later.
Lump sum versus monthly
Rs 12 lakh invested at once at 12% for 10 years grows to about Rs 37.3 lakh. The same Rs 12 lakh paid as Rs 10,000 a month over those 10 years grows to about Rs 23.2 lakh, because most instalments spend far less than ten years invested. That tells you what waiting to pay in steps costs when you already hold the money.
It does not mean a lump sum is better in practice. Most people do not have the full amount on day one, and a SIP spreads the entry price across months. Use the comparison for planning a goal, not to decide to delay investing.
Using the calculator well
Start from the goal and the time you have. Enter a conservative return first, then a higher one, and read the year-by-year table to see the value at milestones. If the figure falls short, the levers are a longer period, a bigger instalment or a step-up; chasing a higher assumed return is the weakest of the three.