Rupee cost averaging is the mechanical effect of investing a fixed amount at regular intervals, and it's the core reason SIPs are recommended so often for volatile investments like equity.
Because you invest the same rupee amount every month regardless of price, you automatically buy more units when the market is down and fewer units when it's up. Over time, this brings your average purchase cost per unit closer to the market's average price over that period, rather than exposing you to whatever the price happened to be on one specific day.
It's important to be clear about what this does and doesn't do: it doesn't guarantee a profit, and it doesn't protect you from a market that only goes down over your entire investment period. What it does do is remove the need to guess when to invest, and it cushions the psychological and financial impact of investing a lumpsum right before a downturn.
The effect is strongest in volatile markets and weakest in markets that rise smoothly and steadily — in a straight-up market, a lumpsum invested on day one would actually outperform a SIP, since all the money was invested at the lowest point immediately.
Frequently asked questions
What is a SIP calculator?
A SIP, or Systematic Investment Plan, calculator estimates the future value of a fixed sum invested every month into a mutual fund, based on an assumed rate of return and the investment duration. It helps you see how disciplined monthly investing compounds over time.
What is the SIP maturity formula?
The formula is FV = P × [((1+i)^n − 1) / i] × (1+i), where P is the monthly instalment, i is the monthly rate of return, and n is the total number of instalments. This accounts for each instalment compounding for a different length of time.
Why does the last instalment earn less than the first?
Because each SIP payment starts compounding only from the month it is invested, the very first instalment enjoys the full duration of growth while the final instalment barely has any time to compound. The total maturity value is the sum of all these differently-aged contributions.