“Even if Trump won every single remaining delegate he could not get to 1237. Due to no chance of winning Montana and South Dakota, Trump is effectively eliminated at the end of May.
Trumps campaign staffers have done this math. That is why they are increasingly laying the groundwork to call for Cruz to exit the race when he is eliminated from a majority. They know Cruz is the second ballot favorite, and that Kasich is a non-factor.”
Here is a calculator that Nate Silver and the crew at FiveThirtyEight.com put up a few days ago.
If you select "Follow the Experts" it fills in the numbers based on the teams best guess, and the total is 1182. In other words 55 short. There are many ways for Trump to gain those 55 from the remaining pool that are plausible. For instance, he might get some of the unallocated delegates, who number 125. Getting 1/2 of them would assure him the nomination.
There is no calculator for "Get Ted to 1237" provided, as it's beyond the realm of possibility.
Handy calculator: