I used numbers, as stated earlier, from Real Clear Politics. Here’s how I arrived at 77%:
There are 4051 pledged delegates. So far, Hillary has 1280 and Bernie has 1030. Subtract those two numbers from 4051 and you get 1741 remaining pledged delegates. Both of them need to get to the majority of 2383 to nominate. Subtract Bernie’s 1030 from 2383 and you get 1353 to win the nomination without any super-delegates. 1353 is 77% of the remaining 1741 pledged delegates. Hillary needs 63%.
Neither can get to 2383 without some super-delegates. Hillary will need less super-delegates than Bernie to reach 2383. She has, so far, 469 of 712 total super-delegates. If those 469 hold, and yes, there’s no guarantee they will, but calculating those into her lead, she needs only 634 delegates of the remaining 1741. Bernie has 31 super-delegates, or 1061 total delegates. He needs 1322 delegates to get to 2383. Twice the amount of Hillary. Which is more probable of getting to 2383 first?