Mathematics • 6 min read

Inflation Adjusted SIP Returns: Real Rate of Return

Information Disclaimer: This article is strictly for educational, factual, and mathematical illustration purposes. It does not contain financial advice, tax guidance, or investment recommendations. All mutual fund investments are subject to market risks.

1. Nominal vs. Real Rate of Return

When projecting long-term returns, it is important to distinguish between nominal values and real values:

  • Nominal Return: The raw rate of return generated by an investment, without adjusting for price inflation. This represents the absolute rupee value.
  • Real Return: The rate of return adjusted for price inflation. This reflects the actual change in purchasing power.

Inflation represents the rate at which the general level of prices for goods and services rises, subsequently eroding the purchasing power of money over time.

2. The Inflation Adjustment Equation

The real rate of return is calculated using the standard **Fisher Equation**:

1 + Real Rate = (1 + Nominal Rate) / (1 + Inflation Rate)

To isolate the **Real Rate of Return**:

Real Rate = [ (1 + Nominal Rate) / (1 + Inflation Rate) ] - 1

Let us calculate the real rate of return assuming a nominal investment return of **12% p.a.** and a consumer price inflation rate of **6% p.a.**:

Real Rate = [ (1 + 0.12) / (1 + 0.06) ] - 1
Real Rate = [ 1.12 / 1.06 ] - 1
Real Rate = 1.0566 - 1 = 0.0566 or 5.66% per annum

3. Numerical Comparison: 15-Year SIP Projections

Let us compare a **₹10,000 monthly SIP** for a duration of **15 years** under two separate compounding calculations:

  • Nominal Projection: Compounded at a nominal rate of 12% p.a.
  • Real Projection (Purchasing Power): Compounded at the real rate of return (5.66% p.a.).
Comparison Metric Nominal Return Projection (12%) Real Return Projection (5.66%)
Total Invested Principal (₹) 18,00,000 18,00,000
Projected Interest Value (₹) 32,45,763 9,87,314
Total Projected Portfolio (₹) 50,45,763 27,87,314

This mathematical comparison shows that while the nominal value of the portfolio at the end of 15 years is projected to be **₹50.45 Lakhs**, its actual purchasing power in terms of today's money is equivalent to **₹27.87 Lakhs**. The difference represents the projected increase in the cost of goods and services over the 15-year period.