A Step-Up SIP's Edge Comes From Its Last Years, Not Its First

The case for a step-up SIP is usually that early increases have the longest to compound, so they do the most work. Run the decomposition and the ordering reverses: the last increments contribute most, despite having least time.

What follows takes a ₹10,000 monthly SIP over 20 years at a 12% annual return, adds a 10% annual step-up, and attributes the resulting difference to the year each increment was added.

The Aggregate Effect Is Large

Flat, the SIP compounds to about ₹92 lakh. With the step-up, the same twenty years produces about ₹186 lakh - roughly ₹94 lakh more, from a schedule that never requires a lump sum.

Break that ₹94 lakh down by which year’s step-up produced it:

Contribution to the step-up SIP’s extra ₹94 lakh corpus, by the year the increment was added - a 10% annual step-up on a ₹10,000 base, 20 years, 12% annual return.

Year Nineteen Beats Year Two by Six and a Half Times

The increment added in year 2 - roughly ₹1,000 extra a month - has nineteen years to compound and contributes about ₹98,000 to the final corpus.

The increment added in year 19 - by then roughly ₹45,600 extra a month, the base having stepped up for eighteen years - has one year to compound and contributes roughly ₹6.5 lakh. Over six and a half times as much, with one-nineteenth of the runway.

The pattern holds monotonically across all twenty years: each successive year’s contribution exceeds the one before it, even as the remaining compounding period shrinks.

Exponential Beats Linear

The mechanism is straightforward once stated. The size of each increment grows exponentially with the step-up rate, while the time left to compound it shrinks only linearly. Exponential growth in the contribution dominates linear decay in the runway.

This also explains a sensitivity worth knowing: the effect is far more responsive to the step-up percentage than to starting a year or two earlier, because the percentage is what drives the exponential term.

The Conclusion Changes, the Recommendation Does Not

A step-up SIP remains worth doing. The aggregate improvement over a flat SIP is real and large, and raising contributions alongside income is a sound habit independent of the arithmetic.

What changes is the reason. “Early increases compound the longest” is a true statement about each rupee and a false explanation of where the corpus comes from - the later increments are simply much larger, arriving when even a short runway operates on a big number.

What This Means for Allocators

Protect the later step-ups first. They are the ones carrying the result, and they are also the ones most likely to be skipped when the instalment has grown to feel large.

Prioritise the step-up rate over the start date when advising on structure. A higher percentage moves the outcome more than an extra year at the front does.

And do not sell the product on the wrong mechanism. The corpus is built at the end of the schedule, which is precisely when investors are most tempted to freeze the contribution.