SIP Returns: XIRR vs. CAGR Explained

CAGR (Compound Annual Growth Rate) is the right tool for measuring the return on a single lump-sum investment. It is the wrong tool for a SIP, because a SIP isn’t one investment — it’s many separate installments, each invested at a different time and each earning a different amount of growth by the end.

Why CAGR breaks down for multiple cash flows

Applying CAGR to a SIP by treating the total amount invested as if it were all invested on day one systematically understates the actual annualized return, because in reality later installments had much less time to grow than the formula implicitly assumes for the whole sum.

XIRR: the correct tool for irregular cash flows

XIRR (Extended Internal Rate of Return) solves for the one constant annualized rate that, when applied to each individual cash flow on its actual date, makes the whole series balance out — correctly weighting installments by exactly how long each one was actually invested.

A verified worked comparison

On a simple example — ₹1,00,000 invested at the start of each of 3 years, redeemed for ₹3,80,000 at year 3 — the naive CAGR calculation reports 8.20%, while the correct XIRR reports 12.29%. The gap exists purely because CAGR assumes all ₹3,00,000 was invested for the full 3 years, when in reality the last installment was only invested for 1 year.

When each measure is the right one to use

Measure	Assumes	Correct for a SIP?
CAGR	One investment, one start date	No
XIRR	Multiple cash flows, each with its own date	Yes

FAQ

Can I calculate XIRR by hand? It requires solving for the root of an equation with no simple closed-form solution — in practice this is done with spreadsheet functions (like Excel’s XIRR) or software, not by hand arithmetic.

Does a higher XIRR always mean a better fund? It means a better annualized return on the specific cash flows measured — useful for comparing your own actual investment timing and performance, though comparing XIRR across different SIPs with very different durations or market conditions still requires some care.

Is XIRR the same as the fund’s published “returns since inception”? Not necessarily — a fund’s own headline return figures are often calculated differently (such as point-to-point NAV growth), while your personal XIRR reflects your own specific contribution dates and amounts, which can differ from the fund’s own reported figures.

Does a step-up SIP make the CAGR-vs-XIRR gap even bigger? Often yes — since a step-up SIP (see the SIP Step-Up Calculator) increases the invested amount over time, later — shorter-duration — installments make up an even larger share of the total invested, widening the gap between a naive CAGR estimate and the correct XIRR.

How does this compare to a lump-sum investment’s return calculation? A lump sum has exactly one cash flow in and one cash flow out, which is exactly the case CAGR was designed for — see the Dollar-Cost Averaging vs. Lump Sum Calculator for how the two contribution styles compare directly.

Why does this matter beyond just knowing the “right” number? Using naive CAGR to evaluate a SIP’s performance can make it look worse than it actually performed, potentially leading to an incorrect comparison against other investment options that were measured correctly.