Tracking Error

Tracking error measures how faithfully an ETF reproduces the returns of what it claims to track. For a spot Bitcoin ETF, the target is the BTC price itself (the benchmark named in its prospectus, often the New York variant of the CME CF Bitcoin Reference Rate). For an S&P 500 ETF, the target is the S&P 500 index. The closer the ETF's daily returns match the target's daily returns, the lower the tracking error.

Two related concepts often used interchangeably (but they are different):

• Tracking difference. The cumulative return gap. If BTC returned 50% over a year and the ETF returned 49.75%, tracking difference is -0.25%. This is the number that matters most for buy-and-hold investors.
• Tracking error. The standard deviation of the daily return difference between ETF and target. Measures how bumpy the tracking is, not just how much off. Important for traders and arbitrageurs.

Sources of tracking gap for a spot Bitcoin ETF:

1. Expense ratio. The issuer's annual fee, accrued daily out of the fund's BTC holdings. US spot Bitcoin ETF fees, per the funds' annual reports filed in 2026:

Product	Ticker	Expense Ratio
Grayscale Bitcoin Mini Trust	BTC	0.15%
Franklin Bitcoin ETF	EZBC	0.19%
Bitwise Bitcoin ETF	BITB	0.20%
VanEck Bitcoin ETF	HODL	0.20%
Ark 21Shares Bitcoin ETF	ARKB	0.21%
BlackRock iShares Bitcoin Trust	IBIT	0.25%
Fidelity Wise Origin Bitcoin Fund	FBTC	0.25%
CoinShares Bitcoin ETF (formerly Valkyrie)	BRRR	0.25%
Invesco Galaxy Bitcoin ETF	BTCO	0.25%
Hashdex Bitcoin ETF	DEFI	0.25%
WisdomTree Bitcoin Fund	BTCW	0.25%
Grayscale Bitcoin Trust	GBTC	1.50%

The Grayscale Bitcoin Mini Trust (BTC) launched in mid-2024 as Grayscale's cheaper sibling product to GBTC, seeded with a portion of GBTC's BTC. At 0.15% it has the lowest fee in the table. (Several issuers cut or waived their fee for a while after launch. iShares charged 0.12% on its first $5 billion for a year, and WisdomTree charged nothing on its first $1 billion for six months. The table shows the standing rates.)

2. Trading costs. When the fund buys or sells BTC for cash creations and redemptions, its execution price can differ from the price used for NAV. At the iShares Bitcoin Trust the AP covers any shortfall rather than the fund, and the fund's annual report notes that such costs may reach shareholders through the share's market price. In-kind creation/redemption takes the fund out of the trade.

3. Custody fees. Typically paid by the sponsor out of the expense ratio rather than charged to the fund on top. The iShares and WisdomTree annual reports, for example, both list the custodians' fees among the costs the sponsor's fee covers.

4. Closing price vs strike. NAV strikes as of 4:00 PM New York (for funds on BRRNY, from trades between 3:00 and 4:00 PM), while the shares trade all day and close at 4:00 PM on the exchange. The two prices are set in different ways, so daily returns on market price and on NAV don't match exactly. This shows up as tracking-error volatility, not as a persistent tracking-difference bias.

Roughly, for a spot Bitcoin ETF:

Annual tracking difference ~ expense ratio + a few basis points

The iShares Bitcoin Trust's annual report for 2025 shows how this plays out. Over the year its NAV per share fell 6.55% while the price of bitcoin fell 6.32%, and the report puts the difference down to its 0.25% sponsor's fee.

Why this matters when comparing Bitcoin ETFs:

• Expense ratio dominates. Over a multi-year hold, a 0.20% fee versus a 1.50% fee compounds into a meaningful gap.
• In-kind vs cash creation/redemption affects trading costs. In-kind, allowed by the SEC on July 29, 2025, takes the fund out of BTC trades when shares are created or redeemed that way.
• Don't confuse expense ratio with tracking quality. Trading costs and pricing differences, items 2 and 4 above, also affect how closely a fund follows bitcoin, so its actual tracking history tells you more than its headline fee.

Tracking error is the boring statistic that tells you whether the ETF is doing its job. For IBIT in 2025, the answer was yes: it trailed bitcoin by about its fee.