Democratic delegates are awarded proportionally, and in states that have voted so far, Hillary Clinton has won more than half of the vote. The absence of winner-take-all states on the Democratic side makes it very hard for Bernie Sanders to close the delegate gap.

If Mrs. Clinton maintains her current level of support in the remaining races, she will earn a majority of the pledged delegates by June 7.

To have a shot at overtaking Mrs. Clinton in pledged delegates, Mr. Sanders would need a series of landslide victories in the few remaining contests, increasing his vote share to about 70 percent, on average.

Mr. Sanders is also significantly trailing Mrs. Clinton in superdelegates, the 714 Democratic Party officials whose support counts toward the nomination. Superdelegates are free to switch candidates at any time before the convention in July; in past elections, they have supported the candidate who has received the most pledged delegates.

If all superdelegates vote for the candidate with the most pledged delegates, Mrs. Clinton will get to 2,383 delgates.

At a news conference this week, Mr. Sanders stated that he and Mrs. Clinton are headed to a “contested” convention since she cannot reach a majority of the delegates with pledged delegates alone. He urged superdelegates in states that he has won to vote for him.

Even if all superdelegates go to the winner of their state — as Mr. Sanders proposes — he still won’t earn enough delegates.

The delegate count as reported by The A.P. lags the total vote somewhat. In the chart below, we are showing delegate estimates from The Green Papers, which include the unallocated delegates from states that have already voted.