As charted on CoinMarketCap.com, Bitcoin Dominance has been under 40% since the start of the year 2018.
Dominance is defined as percentage of total market capitalization.
Ethereum, Bitcoin Cash, Litecoin, Ripple, Dash, NEM, Monero, IOTA, Neo and others are the cryptocurrencies that have been chipping away at BTC’s dominance.
As recently as January 2016, Bitcoin was still enjoying 90 percent dominance. By March 2017, the percentage dropped below 70 percent. The first time it dipped below 50 percent was in May 2017. It dipped below 40 percent in June before rebounding in the suceeding months, only to again fall below 40 again in December 2017.