If Trump has 500 more delegates than Cruz (presuming Kasich doesn’t pick up any more) then he will have over 1237. Here’s the math:
2474 Total available delegates
661 Current Trump
406 Current Cruz
142 Current Kasich
169 Current Rubio
1096 Remaining
255 Trump current lead
So as of today, Trump has 255 more delegates than Cruz. That means out of the remaining delegates, Trump would need 250 more delegates than Cruz to reach “500 more than Cruz”
548 Half of the remaining delegate total
If they were each getting half the remaining we’d add this to their current total, right? But they’re not. To get Trump to “500 more than Cruz at the end”, he needs to get 250 more than Cruz out of what remains. To get there, we can add 125 of that half to Trump and subtract 125 of that half from Cruz.
673 125 more than half remaining delegates
423 125 less than half remaining delegates
Then we add them to the existing totals and get...
1334 Trump total to be 500 delegates ahead of Cruz
829 Cruz total to be 500 delegates behind Trump
So to sum up, if Trump has 500 more delegates than Cruz he’ll win the nomination outright. To be specific, if Trump has anything more than 211 delegates than Cruz, he will win the nomination outright.
For Trump to win outright, he needs to win ~52% of the remaining delegates.
That 2nd to last sentence is unclear. It should say “If Trump wins 211 more delegates than Cruz out of what remains, then he wins the nomination outright.