WASHINGTON (AP) — While President Joe Biden and former President Donald Trump are the overwhelming favorites to once again win their parties’ nomination for a second term, they’re not the “presumptive nominees” just yet.

Though you may hear the term more frequently in the coming days, The Associated Press only uses the designation once a candidate has captured the number of delegates needed to win a majority vote at the national party conventions this summer. That point won’t come until after more states have voted. The earliest Trump could clinch the nomination is March 12; for Biden, it’s March 19.

Trump on Saturday is looking to win his fourth straight early contest, as he faces former United Nations Ambassador Nikki Haley in her home state of South Carolina. Trump easily won in Iowa, New Hampshire and Nevada, where he and Haley did not face each other on the ballot.

Biden notched commanding victories in South Carolina and Nevada earlier this month. He also won as a write-in candidate in New Hampshire, after he refused to campaign or appear on the ballot.

A presidential candidate doesn’t officially become the Republican or Democratic nominee until winning the vote on the convention floor. It hasn’t always been this way. Decades ago, presidential candidates might have run in primaries and caucuses, but the contests were mostly ornamental in nature, and the eventual nominees weren’t known until delegates and party bosses hashed things out themselves at the conventions.

Today, the tables have turned. Now, it’s the conventions that are largely ornamental, and it’s the votes cast in primaries and caucuses that decide the nominees. Because of this role reversal, for the last half-century or so, the eventual nominees were known before the conventions, sometimes long before the conventions or even long before they’d won enough delegates to unofficially clinch the nomination.

Nonetheless, the AP won’t call anyone the “presumptive nominee” until a candidate has reached the so-called magic number of delegates needed for a majority at the convention. That’s true even if the candidate is the only major competitor still in the race.

For Republicans, that magic number is 1,215; for Democrats, it’s more of a moving target but currently stands at 1,968.