What AUM means

AUM — assets under management — is the total market value of everything a mutual fund scheme holds, less its liabilities: all the shares, bonds and cash in the portfolio, marked to today’s prices. It is the size of the pot.

The first mutual fund post defined NAV as that pot divided by the number of units. So:

AUM  =  NAV per unit × Units outstanding

which means AUM changes for two entirely different reasons: units change (investors buy or redeem) or NAV changes (the market moves). Fund marketing tends to present AUM growth as evidence of investor confidence. Often it’s just the index going up.

Worked example: the market moves the AUM by itself

Take a fund with ₹10,000 crore of AUM at the start of a financial year and assume nobody buys or sells a single unit all year. Its AUM at year-end is simply the starting AUM times the NAV change. Here it is on the UTI Nifty 50 Index Fund’s actual NAV path (source: AMFI via mfapi.in; data to 31 March 2026). Each row starts fresh from ₹10,000 crore, so the two years can be read side by side rather than chained:

Year NAV change AUM at year-end, zero flows (from ₹10,000 crore)
FY25 (Apr 2024 – Mar 2025) 6.26% ₹10,625.82 crore
FY26 (Apr 2025 – Mar 2026) −4.27% ₹9,572.94 crore

Historical data, for illustration only. The point isn’t the fund; it’s that a headline like “AUM fell 4%” or “AUM grew 6%” is uninformative until you know how much of it was flows. The number that tells you what investors did is net inflow — AMFI publishes it monthly, by category — not AUM.

Where size genuinely matters

Fees. SEBI caps what an open-ended scheme can charge, in slabs that fall as AUM rises. The logic is that running a ₹20,000 crore fund doesn’t cost forty times what running a ₹500 crore fund does. Under the SEBI (Mutual Funds) Regulations, 2026, in force from 1 April 2026, the cap is on the base expense ratio (BER), and for open-ended equity-oriented schemes other than index funds, ETFs (exchange-traded funds) and funds of funds it is, per the daily net assets in each slab (SEBI (Mutual Funds) Regulations, 2026, regulation 66(7)(c), 66(9) and 67):

AUM slab Maximum base expense ratio
First ₹500 crore 2.10%
Next ₹250 crore 1.90%
Next ₹1,250 crore 1.60%
Next ₹3,000 crore 1.50%
Next ₹5,000 crore 1.40%
Next ₹40,000 crore reduced by 0.05% for every ₹5,000 crore of net assets, or part of it
On the balance of the assets 0.95%

Index funds and ETFs are capped at 0.90% of daily net assets regardless of size. The base expense ratio leaves out statutory levies and transaction costs, and a scheme may charge brokerage on top of it, up to 0.06% of trade value in the cash market and 0.02% in derivatives. So the total expense ratio an investor sees can sit above the base figure. Before 1 April 2026 the 2018/19 framework capped the total expense ratio, starting at 2.25% on the first ₹500 crore, so the two sets of numbers are not directly comparable. The shape is the same: the cap falls as the fund grows. The practical consequence is that as a fund grows, its maximum permitted fee falls. Whether the fund actually charges less is a different question — the cap is a ceiling, not a price — and the expense ratio post is where to check what you’re really paying.

Liquidity. A large fund can’t buy meaningful positions in small companies without moving their prices. A ₹50,000 crore small-cap fund putting 2% into a company with a ₹1,000 crore market cap would own the whole company. This is why very large small- and mid-cap funds sometimes stop accepting lump sums, and why “biggest fund in the category” is not a compliment in every category.

Nothing else. AUM says nothing about returns, risk or quality. The rolling returns and drawdown posts don’t mention size once, and that’s not an oversight.

🧒 Explain it like I'm 10 (optional — skip if this is already clear)

AUM is what everything in a shop’s storeroom is worth.

That number goes up when new stock arrives (inflows). It also goes up when the price of what’s already there rises, with nothing new arriving. So when the shop says “our storeroom is worth 6% more!”, ask: new stuff, or just higher prices?

Common mistakes

  • Reading AUM growth as inflows. Separate the two. In a year the index rose 6%, an unchanged fund’s AUM rose 6%.
  • Treating big as safe. Size buys lower fee caps and nothing else. A large fund fell exactly as far in 2008 as a small one holding the same stocks.
  • Ignoring size where it bites. In small- and mid-cap categories, AUM relative to the size of the companies held is a real constraint.
  • Comparing AUM across categories. A ₹5,000 crore liquid fund is small; a ₹5,000 crore small-cap fund is large. Same number, opposite meaning.

Takeaway: AUM is NAV times units — the market value of a fund’s pot — and it moves with the market whether or not anyone invests a rupee. It sets the regulator’s fee ceiling and constrains what a small-cap fund can buy; it says nothing about whether the fund is any good.