US spot bitcoin and ethereum exchange traded funds added about $23 billion of assets last week. Investors put in $2.6 billion.

Both numbers are true and they describe completely different things. The first is what the funds are worth. The second is what people bought.

The arithmetic

Bitcoin ETFs took $1.92 billion of net inflows in the week to 21 August, and their assets under management rose from $76.6 billion to $96.1 billion, an increase of 25.4 percent. Ethereum ETFs took $697.2 million and grew from $10.5 billion to $14.3 billion, up 35.9 percent.

Subtract the money that came in from the money the funds gained and the difference is about $20.7 billion. That is price appreciation: bitcoin rose roughly 24 percent over the week and ether roughly 30 percent, and a fund that holds an asset gets richer when the asset does, without anyone buying a share.

Check it directly. Bitcoin funds started the week holding $76.6 billion. A 23 percent rise on that stock alone accounts for about $17.6 billion of the $19.5 billion increase. The inflows are the remaining $1.9 billion. The same works for ether.

Why the distinction matters

Assets under management measure the size of a fund. Flows measure demand for it. Only one of them is evidence about what investors are doing, and it is the smaller one.

The confusion has a direction. In a rising market, AUM growth always exceeds inflows, sometimes by an order of magnitude, and quoting the larger figure makes demand look far stronger than the flow data supports. In a falling market the same arithmetic runs the other way, and funds that are taking in money can appear to be shrinking.

Neither is a conspiracy. It is what happens when a stock and a flow get reported in the same sentence without being labeled.

This is the same failure mode we described this morning in bitcoin's record dollar-denominated weekly gain, where a record in currency units turned out to be mostly a fact about the price level. The habit that fixes both is identical: ask what the number would be if the price had not moved.

What the flows do say

$2.6 billion in a week is not a small number, and it is genuine demand. It is roughly 2.5 percent of the combined ending assets, which is a meaningful weekly addition for any fund complex.

The concentration is the more interesting detail. BlackRock's IBIT took the largest share of new money, at one point capturing 83 cents of every dollar that went into bitcoin funds in a single day.

That is a market where the flows are not spread across issuers but are collapsing into one product. For an investor it means the liquidity and the spreads are likely to be best there and to keep getting better, which is self-reinforcing. For the industry it means the economics of running a competing spot bitcoin ETF are difficult, since these products differentiate mainly on fee and scale, and one competitor has both.

The sentence to be careful with this week

"Twenty-three billion dollars flowed into crypto ETFs" is the version of this that will circulate. It is wrong by a factor of about nine.

The correct version is that $2.6 billion flowed in and the assets already there went up in value. If the price gives back the week, the $20.7 billion goes with it, and the $2.6 billion is what will still have been bought.

This story explains published fund data and is not investment advice.