Rupee Cost Averaging — Watch It Work

What Is Rupee Cost Averaging and How Does It Work?

Rupee Cost Averaging (RCA) is the automatic mechanism by which a fixed monthly SIP buys more mutual fund units when NAV is low and fewer units when NAV is high. Because the investment amount is fixed in rupees rather than in units, a falling market is not a threat to a SIP investor — it is an opportunity. Every month of declining NAV means more units are acquired at a cheaper price, lowering the investor's average cost per unit over time.

The mathematics are straightforward. If a ₹10,000 SIP buys units at NAV ₹100, it acquires 100 units. If the next month NAV falls to ₹70, the same ₹10,000 buys 142.86 units — 43% more units for the same money. If NAV falls further to ₹50, the SIP buys 200 units. By the time the market recovers and NAV returns to ₹100 or higher, the investor holds a large number of units acquired at an average cost well below the current NAV. This gap between average cost and current NAV is the source of RCA's return advantage.

Why Is a Market Crash the Best Time to Continue Your SIP?

This is the most counterintuitive truth in mutual fund investing, and the simulation on this page demonstrates it precisely. During the crash phase of the simulation — as NAV falls from ₹130 to ₹68 — each ₹10,000 SIP buys an increasing number of units. The months at the bottom (NAV ₹68 to ₹73) are the most valuable months in the entire 30-month simulation, because the units acquired then are the ones that grow most dramatically during the recovery.

An investor who pauses or stops their SIP during a crash misses exactly these months. They protect themselves from the psychological discomfort of investing when the portfolio is underwater, but they pay for that comfort with significantly lower returns. Every major market crash in India — 2008, 2011, 2015, 2020 — has been followed by full recovery and new highs. Investors who continued SIP through each of these corrections ended up with more units at lower average costs, and substantially higher wealth at the recovery.

How Does Rupee Cost Averaging Compare to Lump Sum Investing?

The comparison between SIP with RCA and lump sum investing depends heavily on market timing. A lump sum invested at a market peak (as in this simulation, at NAV ₹130) is immediately exposed to the full depth of the crash. The investor holds the same number of units throughout the decline and recovery, with no ability to benefit from lower prices. A SIP investor, by contrast, keeps adding units at every price point — including all the cheapest prices during the crash bottom.

The lump sum investor will still profit if they hold through the full recovery — at NAV ₹170, even the peak-price lump sum investor has made money. But the SIP investor who entered at NAV ₹100 and continued through the crash will have a lower average cost and a higher total unit count, producing a superior final corpus from the same total investment amount. The advantage of RCA is largest when the market goes through a significant crash and recovery during the investment period — which, over any 10 to 20 year investment horizon in India, is virtually guaranteed to happen at least once.

What Is the Average Cost Benefit from a SIP Over a Full Market Cycle?

In the demonstration on this page, a ₹10,000 monthly SIP over 30 months invests a total of ₹3 lakh. The NAV journey goes from ₹100 (start), peaks at ₹130, crashes to ₹68, bottoms sideways, recovers, and reaches a new high of ₹170. The average NAV over the 30 months is approximately ₹109. But the average cost per unit for the SIP investor — because more units are purchased at lower NAVs — is approximately ₹93 to ₹97, meaningfully below the simple average. This is the quantifiable benefit of rupee cost averaging: a lower average cost than the arithmetic mean of prices, achieved automatically without any market timing.