According to calculations by cookpolitical.com, Trump could reach 1400 delegates by June 7th. Well before the convention:
Donald Trump’s breathtaking romp through the Northeast corridor on Tuesday points to a fundamental shift in the GOP race. Once thought of as a candidate with a low ceiling, Trump won all but eight of the 119 bound delegates at stake in Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island. His smallest margin of victory was 30 points, and he carried all 34 congressional districts and all 107 counties.
For the first time since mid-March, he’s ahead of where we estimate he needs to be to reach 1,237 delegates and clinch the GOP nomination. In fact, current polling in the remaining ten states is consistent with a scenario in which Trump could capture as many as 1,400 delegates by June 7. Indiana is now a must win for Ted Cruz and the #NeverTrump movement, but the odds of a contested convention have dramatically declined.