The web will account for 21.5% of the approximately $555.16 billion that marketers will spend globally on advertising spending in 2014, crossing the 20% threshold for the first time, according to an advertising forecast from Zenith Optimedia. The marketing agency, which tracks advertising spending, predicts online ad spending will reach $119.39 billion next year.

Spending on paid search advertisements will account for nearly half of that online ad spending, 48.4%, slightly less than the 49.1% it predicts marketers will spend on it this year. That’s because spending on display advertising is on the rise, the agency says. Zenith Optimedia predicts display ads will account for 39.9% of online ad spending in 2014 versus 38.4% this year. The shift is largely because of the growth of social media and online video display advertising, it says.

Within display spending, Zenith Optimedia predicts advertising on social media sites will grow 27.3% between 2013 and 2014. It anticipates spending on paid search, meanwhile, will grow 16.1% during the same time frame.

Web ads already command for more than 25% of advertising spending in six nations: Canada, Norway, South Korea, Sweden and the United Kingdom, the agency says. In 2011, U.K. marketers spent 33% of their advertising budgets on the web. Zenith Optimedia predicts this share will rise to 39% next year.

In the United States, retailers account for the single largest chunk of online ad spending, according to the Interactive Advertising Bureau, a trade group for the online advertising industry. Retailers spent $7.31 billion on online advertising in 2012, accounting for 20% of all online advertising spending. In 2011, retailers spent $6.98 billion on web ads. Search ads accounted for 46.3% of all online ad spending in the United States in 2012. Display advertising accounted for 33.0% of all online ad spending in the United States in 2012.