How To Calculate SIP Corpus

A Systematic Investment Plan is a way of investing a fixed amount in mutual funds at regular intervals, usually monthly. Instead of timing a lump sum, you spread contributions across the year and let each one compound.

The maths is an annuity. Every monthly instalment earns a return for the months that remain until the end of the term, and because instalments are made throughout the period, the early ones earn for much longer than the late ones.

The corpus at maturity is the monthly instalment multiplied by the annuity factor, which is one plus the monthly rate raised to the number of months, minus one, divided by the monthly rate.

The monthly rate is the expected annual return divided by twelve. It is an approximation of the true monthly compounding rate, but it is the convention used for SIP projections and keeps the arithmetic simple.

The amount you actually invested is the instalment times the number of months. The gains are the corpus minus that amount, and over a long term the gains can approach or exceed the money you put in.

SIPs are popular because of rupee-cost averaging. When the market is down your fixed instalment buys more units, and when it is up it buys fewer, which smooths the average purchase price over time.

Averaging does not guarantee a profit, but it removes the pressure of picking a single entry point. It also turns investing into a habit rather than a decision you have to make each month.

The expected return is the most sensitive input. A one percentage point change in the assumed return moves the final corpus by a meaningful amount over ten or twenty years, so treat the figure as a scenario rather than a forecast.

Time matters more than the instalment size. Because compounding is exponential, extending the term by a few years often adds more to the corpus than increasing the monthly amount, which is why starting early is the single most powerful lever.

The step-up variant increases the instalment each year, usually in line with your income. Even a modest annual step-up lifts the corpus noticeably over a long horizon, because the larger contributions also compound.

Mutual fund returns are not guaranteed. Equity funds can fall sharply in a bad year, and the smooth growth curve a SIP projection implies is an average, not a path. Plan for the volatility that sits behind the average.

Expense ratios and exit loads reduce the return you keep. A fund charging one percent a year hands you roughly one percent less than its gross return, so the return you enter should be net of costs.

A SIP works best alongside a lump sum rather than instead of one. If you have a large amount to invest, staggering it in over a few months reduces timing risk, but the money waiting on the sidelines earns nothing in the meantime.

The calculator models the instalment, the return and the term you enter and nothing more. It assumes a constant return and no missed instalments, so treat the output as an estimate and revisit it as your income and goals change.