Compare Crypto Returns on the Same Clock

Two crypto charts can look comparable while measuring different things. One may show a rolling 24-hour change in US dollars; another may show the change since midnight in USDT. One may use a composite price, while the other follows a single exchange. Putting the percentages side by side does not repair those differences.

A fair comparison begins before the chart is drawn. Choose the instrument, price source, quote currency, observation interval and exact endpoints. Then use the same choices for every series. This is a measurement exercise, not a method for predicting which asset will outperform next.

The dataset: one venue and 31 completed daily candles

CryptX retrieved Bybit spot BTCUSDT and ETHUSDT daily candles on 22 September 2026 at 19:31 UTC. We requested data ending before 22 September began and retained 31 matching daily candle dates, 22 August–21 September 2026. Each date is the candle’s UTC opening date; its close belongs to the end of that day.

The series contains 30 close-to-close daily returns. The close labelled 22 August is our starting observation, not the opening price on 22 August. That distinction matters when someone tries to reproduce a reported “one-month” result.

Bybit’s REST documentation says candle results are ordered by starting time and that an unfinished candle’s close field is its last traded price. We sorted the returned data into chronological order and excluded the unfinished 22 September candle. The WebSocket documentation separately documents a confirmation flag for completed candles; that flag was not included in this connector output.

These prices describe one venue’s historical spot pairs. They are not dollar conversion rates, executable quotes for a particular order size, or the prices at this article’s publication time.

Put both starting observations at 100

Plotting Bitcoin near 80,000 and Ether near 2,500 on one ordinary price axis makes their nominal units dominate the picture. Instead, divide every close by that asset’s first retained close and multiply by 100.

Both indexed lines begin at 100. Bitcoin ends at approximately 112.39, and Ether at 114.59. An indexed value of 114.59 means a 14.59% increase from the selected starting close. It does not mean the coin costs 114.59 USDT.

The difference in endpoint returns is approximately 2.20 percentage points. If the question is how ETH performed relative to BTC as a ratio, calculate the ratio of their growth factors instead: 1.14594 divided by 1.12391, minus one, approximately 1.96%. Percentage-point outperformance and relative-ratio growth are related but different quantities.

Rebasing makes the chosen path legible without answering every investment question. It does not account for trading fees, staking income, taxes, custody costs or the possibility that an investor bought at a different time.

High co-movement can coexist with different returns

For each pair of adjacent closes, we calculated a simple daily return: the newer close divided by the previous close, minus one. The Pearson correlation across the 30 synchronized BTC and ETH daily returns was approximately 0.91.

NIST defines this correlation coefficient as a measure of linear relationship. Here it summarizes how these two sets of daily changes moved together within the selected sample. It does not say that Ether moved 91% as much as Bitcoin, that 91% of trading days were positive, or that one asset caused the other to move.

The sample is short and contains only one selected market period. A larger dataset, another interval or a different market regime could produce a different estimate. These observations support a description of that window, not a permanent correlation assumption for portfolio construction.

Notice that we correlated returns, not the two nominal price levels. Two price paths can both trend upward and produce an impressive level correlation even when that statistic is poorly suited to the co-movement question being asked.

Keep the quote currency visible

Both pairs here are quoted in USDT. Sharing that denominator makes the pairwise comparison internally consistent, but it does not make USDT identical to a US dollar at every instant.

An aggregate USD series may incorporate exchange-rate conversions and multiple trading venues. CoinGecko’s methodology, for example, describes price aggregation and conversions rather than simply treating every stablecoin quote as an unconditional dollar price. Swapping that series into one side of our chart would change the experiment.

For a USD performance comparison, use a documented USD source or convert every retained observation with aligned USDT/USD data. Applying one final conversion rate to an entire historical path does not reconstruct the currency effect through time.

Ask what the chart leaves out

The SEC’s educational bulletin on performance claims encourages readers to examine periods, benchmarks and excluded fees. Those are useful questions for crypto charts as well, without implying that these spot assets are mutual funds or that one legal framework applies to every reader.

A reproducible comparison should retain the original closes, their timestamps, the calculation formula and the missing-data policy. If a date is absent, disclose it and align the remaining observations; do not quietly carry a price forward and call the resulting zero change an observed return.

This case study preserves a specific historical window. Its lasting value is the procedure: align the clocks, name the market, calculate the same quantity, and keep the limitations beside the result.

To see why a reference-price chart differs from the result of an actual swap, read slippage, price impact and minimum received.