One formula, three moving parts
Dominance is Bitcoin’s circulating market capitalisation divided by the capitalisation of the whole crypto market, multiplied by 100. Market capitalisation is price times circulating supply. If BTC is valued at 500 units and all other tracked assets together at 500, its share is 50%. This is a share of measured value, not a share of trades, users or cash deposited.
Real share changes, with the BTC return alongside
CoinGecko reports BTC dominance falling from 87.2% to 38.9% through 2017 and from 69.5% to 38.2% through 2021. In 2021 Bitcoin itself gained 62.6% in USD: the market around it grew faster. In Q1 2025 the opposite lesson appeared: BTC dominance rose 4.6 percentage points to 59.1% while BTC fell 11.8%. Other assets lost proportionally more; a higher share was not a profitable BTC quarter.
How to read this chart
- Each bar is a market-share snapshot at the beginning or end of its year. The bar is not a price chart.
- The separate Q1 2025 panel uses a different interval: dominance rose although BTC lost value in dollars.
- The interactive figures below are hypothetical capitalisations, not a continuation of the historical series.
2017
2021
CoinGecko · Bitcoin dominance history
BTC.D 69.5% → 38.2%
CoinGeckoBTC.D +4.6 percentage points → 59.1%
CoinGeckoFour ways to read the same line
A dominance line tells you only about a fraction. Combine its direction with BTC’s dollar return and, for a particular altcoin, the coin’s return against BTC. The four combinations below are descriptions of possible outcomes, never buy or sell signals.
Share ↑ · BTC price ↑
BTC is gaining value and market share. This alone does not tell you whether every altcoin fell in dollars.
Share ↓ · BTC price ↑
BTC gained, but the rest of the tracked market grew faster. This happened in 2021; inspect the coin you care about separately.
Share ↑ · BTC price ↓
BTC fell, but the rest lost relatively more. Q1 2025 is a real example; higher dominance did not mean profit.
Share ↓ · BTC price ↓
BTC fell and its share shrank too. Other assets may have held up better, including stablecoins; do not assume altcoins rose.
A simple market-cap model
Change the illustrative market capitalisations. The starting market is 500 units of BTC and 500 of everything else: 50%. The presets demonstrate how the share changes when only the denominator grows or when both groups shrink. These are made-up values to teach the arithmetic, not historical market data.
Illustration only · arbitrary units · not live market data
What changes the denominator
The denominator includes the assets counted by the data provider. CoinGecko’s breakdown explicitly includes stablecoins. Their circulating supply can grow even when speculative altcoins are weak. New listings and token supply changes also shift measured market cap. Compare like-for-like sources and do not call every decline in BTC dominance an altcoin season: breadth requires checking how many eligible coins actually beat BTC over the same period.
Five checks before a conclusion
First choose the same dates for each graph. Then compare BTC.D with BTC/USD, the specific coin against BTC, and the market’s composition. Distinguish percentage points of share from percent returns: a move from 50% to 40% is minus 10 percentage points, or a 20% relative decline in the share. Neither number describes your portfolio return.
- 01Read the same period and provider on all charts.
- 02Check BTC’s return in dollars, not only BTC.D.
- 03Check the chosen altcoin against BTC and against USD.
- 04Look at stablecoin weight, new tokens and changes in circulating supply.
- 05For “altseason”, check broad 90-day outperformance, not just one line.
Original sources
The historical numbers below come from CoinGecko’s published research for distinct periods, not a reconstructed continuous BTC.D series. The calculator is purely illustrative. Exact readings can differ between providers because asset coverage and circulating supplies differ; record the provider, time range and measure before drawing a conclusion.
This guide explains a measurement; it does not forecast prices or recommend a trade.