Dow goes from 37,000 to 38,000 in just 40 days. A history of the Dow and big round numbers

The Dow Jones Industrial Average crossed the 38,000 mark for the first time on Monday, just 40 calendar days after its previous round-number milestone.

The round-number threshold is the latest of a string of milestones on Wall Street, which last week saw the S&P 500 set a record high and confirm a new bull market.

The Dow's thousand-point milestones serve as a short-hand history of Wall Street.

The average number of days between thousand-point milestones have gotten shorter over time, as the percentage gain required to hit each new level declines. The gaps are particularly small during big market rallies, when the Dow can take out several new levels in quick succession.

For example, the Dow crossed seven thousand point barriers within 12 months during the pandemic-era market rally that gained steam in the second half of 2020.

When the Dow crossed 37,000 on Dec. 13, it was the first new thousand-point mark in 771 days. The biggest percentage gains in the average since that day have came from insurance giant Travelers and Merck, according to FactSet.

The Dow, which is weighted by share price and consists of just 30 stocks, is not considered the best representation of the U.S. stock market but does hold historical importance on Wall Street.