It's a common source of confusion: a mutual fund's fact sheet advertises a certain annualized return, but when you check your own SIP (Systematic Investment Plan) in that same fund, the return shown is different -- sometimes better, sometimes worse. Neither number is wrong. They're measuring two different things.
A fund's return assumes a lump sum, on day one
When a fund reports its 5-year or 10-year annualized return, that figure is almost always calculated as if you invested one lump sum on the first day of the period and left it untouched until the last day. It's a clean, comparable number precisely because it removes timing from the equation.
A SIP doesn't work that way. You're investing a fixed amount every month, which means each installment buys units at a different price and has a different amount of time to grow before the measurement date. Your money isn't one lump sum -- it's dozens of smaller lump sums, each with its own start date.
This is what rupee cost averaging actually means
Rupee cost averaging (the same idea is called dollar cost averaging elsewhere) is simply the natural result of investing a fixed amount on a schedule: when the price is high, your fixed amount buys fewer units; when the price is low, it buys more units. Over time this means you're not betting your entire investment on getting the timing right on a single day.
It's often described as if it guarantees a smoother or better outcome, but that's not quite right either -- it's a byproduct of periodic investing, not a strategy for improving returns on its own. If the fund's price trends steadily upward the whole time, a lump sum invested on day one would have outperformed the SIP, because more money would have been invested at the lowest price. Rupee cost averaging genuinely helps you avoid the worst outcome (putting everything in right before a drop), but it doesn't hand you the best outcome either.
Why the correct SIP return uses XIRR, not CAGR
Because each SIP installment has a different investment date, comparing your SIP's total return to the fund's CAGR (Compound Annual Growth Rate) is comparing two different kinds of math. The correct way to measure a SIP's actual annualized return is XIRR (Extended Internal Rate of Return), which accounts for the exact date and amount of every individual installment, plus the current value. This is why some platforms show you an XIRR figure alongside your SIP instead of a simple CAGR -- it's the only fair way to answer the question of what annual rate your actual cash flows earned.
What this means practically
If you're comparing your SIP's performance to a fund's advertised return, don't expect them to match -- they're structurally different calculations, not evidence that something went wrong. What actually matters is whether your money grew at a rate consistent with the fund's underlying performance over the periods your installments were actually invested.
Projecting where a SIP is headed
If you want to see what a monthly SIP could grow into at a given expected annual return, the SIP Calculator computes the maturity amount for you -- useful for planning ahead, though remember it projects a constant assumed return, while a real fund's actual month-to-month returns will vary the way described above.