The question XIRR answers
Real investing is messy: a SIP here, a lump-sum top-up there, a partial withdrawal for an emergency. Ask "what return did I actually make?" and simple formulas fall apart, because every rupee has been invested for a different length of time. XIRR resolves the mess with one clean definition, it is the annual rate r for which
Σ CFᵢ / (1 + r)^(dᵢ/365) = 0
where each cash flow CFᵢ is weighted by dᵢ, its exact number of days from the first flow (the actual/365 convention). Money you put in is negative, money you received, plus the current value of what you still hold, is positive. There is no algebraic solution; the calculator, like Excel, iterates until the equation balances.
The canonical example
Excel's documentation uses this cash-flow set, and it is a good test case:
| Date | Cash flow | Meaning |
|---|---|---|
| 1 Jan 2008 | −10,000 | Investment |
| 1 Mar 2008 | +2,750 | Return |
| 30 Oct 2008 | +4,250 | Return |
| 15 Feb 2009 | +3,250 | Return |
| 1 Apr 2009 | +2,750 | Return |
13,000 came back on 10,000 invested, a 30% total gain, but compressed into about 15 months, which annualises to 37.34%. That compression is the whole point: XIRR prices the calendar, not just the amounts.
XIRR vs CAGR: when each applies
CAGR is valid for exactly one pattern, a single lump sum in, a single value out. For that pattern, XIRR and CAGR agree. Add even one intermediate flow and CAGR loses its meaning, because "the" holding period no longer exists. Practical rule:
- Lump sum, held untouched → CAGR (or XIRR, they match).
- SIP, top-ups, withdrawals, dividends reinvested by you → XIRR, no substitute.
- Comparing your result to a fund factsheet → your XIRR vs their point-to-point return measures your timing as well as their management; the two legitimately differ.
This is why every serious SIP platform reports XIRR. Your monthly instalments, modelled cleanly in the SIP calculator, each carry a different holding period, and only XIRR aggregates them honestly. The same logic applies in reverse to withdrawals: a SWP is a stream of dated positive flows, and XIRR is again the right yardstick.
Reading the number
A negative XIRR means the dated flows lost money at that annual pace, common and not alarming early in a SIP, when a market dip hits instalments that have barely had time to grow, and annualisation stretches a small loss into a scary rate. Symmetrically, a huge positive XIRR over a few months (a 5% gain in 30 days is ~80% annualised) is arithmetic, not prophecy. XIRR earns its keep on periods of a year or more, where annualising describes rather than extrapolates. And remember it reports a nominal rate: at 6% inflation, a 10% XIRR is roughly 4% real, the usual haircut applies before celebrating.