Step-up SIP calculator:
how a yearly increase builds a bigger corpus

What a step-up SIP is

A step-up SIP raises your monthly instalment by a fixed percentage or amount, usually once a year. You start at a level that is comfortable today and let the instalment grow as your income does.

It addresses a common problem with a flat SIP. An amount that felt large at 25 can feel small at 35, and most people never get round to increasing it. A step-up builds the increase into the plan from the beginning.

You can step up by a percentage or by a fixed amount. A 10% step-up lifts ₹5,000 to ₹5,500 and then ₹6,050. A fixed step of ₹500 lifts it to ₹5,500 and then ₹6,000. Over ten years the percentage version reaches ₹11,790 and the fixed one ₹9,500, so a percentage step asks more of you in the later years.

It suits salaried people with predictable raises. If your income is irregular, a SIP you can pause or reduce may serve you better than a schedule that assumes yearly increases.

The calculator needs four inputs: the starting amount, the yearly step-up, the number of years and an assumed return. The first three are decisions; the fourth is a guess, so test more than one value.

Step-up SIP formula

1. 1Write down the starting amount, the step-up rate and the assumed annual return.
2. 2Work out the instalment for each year by multiplying by (1 + step-up rate) once per year.
3. 3Convert the return to a monthly rate and value each year's twelve instalments at that year's end.
4. 4Add the previous balance, carried forward by twelve months of growth, to get the new year-end value.

In words: carry the previous year's balance forward by twelve months of growth, then add that year's twelve instalments valued at the year-end. Repeat for each year. The final Vᵧ is the projected corpus.

Example: ₹5,000 with a 10% yearly step-up for 10 years at an assumed 8%

A flat SIP of ₹5,000 for the same ten years at 8% reaches ₹9,14,730 on ₹6,00,000 invested. The step-up version puts in ₹3,56,245 more and ends ₹4,55,096 higher.

Another way to see it: a flat SIP would need to be about ₹7,488 a month from day one to reach the same corpus. The step-up lets you start at ₹5,000 and arrive at the same place by increasing in small steps.

Per rupee invested, the step-up plan returns about 1.43 times what went in, against 1.52 times for the flat plan, because the rupees added in later years have had less time to grow. A larger corpus is not the same as a better rate.

Checkpoints help when you recompute by hand. After five years the projected value is about ₹4,41,829 on ₹3,66,306 invested, so roughly a third of the final corpus is built in the first half.

The instalment, year by year

The instalment crosses ₹10,000 in year 9 and reaches ₹11,790 in year 10, more than double the start. The amount invested in the final year, ₹1,41,477, is more than twice the first year's ₹60,000.

Step-up versus flat SIP at different step-up rates

A step-up of 5% adds about ₹2.0 lakh over a flat SIP; 10% adds about ₹4.6 lakh. The gain comes from putting more money in, mostly in the later years when it has less time to grow, not from a higher rate of return.

Be honest about what the step-up buys. A flat SIP at the step-up's average instalment of about ₹7,969 invests the same total and would end near ₹14.58 lakh, about ₹0.9 lakh more than the ₹13.70 lakh above, because its money goes in earlier. The step-up's advantage is affordability: it lets you start small and still reach a similar place.

The step-up version leads at every assumed return. At 12%, for example, it projects about ₹16.70 lakh against ₹11.50 lakh for the flat SIP, but the extra ₹3.56 lakh invested explains much of that gap.

Choosing a step-up you can keep

The risk with a large step-up is that it outgrows your income. Suppose your take-home pay is ₹50,000 and the ₹5,000 SIP is 10% of it. If pay grows 5% a year, it is about ₹77,566 in year 10, and a SIP of ₹11,790 would take about 15% of it.

Work the check the other way round. Pick the share of take-home you are willing to invest at the end, then see what step-up gets you there. Linking the step-up to your realistic pay rises makes the plan one you can keep.

It is also fine to skip a step in a hard year. One missed increase does little damage; abandoning the SIP altogether does a great deal.

• Start with a step-up at or below your expected yearly pay rise.
• Re-check the instalment each year and adjust the next step if your income changed.
• Keep the emergency fund and insurance paid before raising the SIP.

Mistakes when planning a step-up SIP

• Choosing a step-up from a calculator default without checking what the final-year instalment will be.
• Applying the percentage to the monthly amount every month instead of once a year.
• Comparing a step-up corpus with a flat SIP without noting the extra money invested.
• Assuming the assumed return is guaranteed, or using the same figure for every scenario.
• Forgetting that your fund house may need a separate instruction or a top-up facility to step up automatically.