a good bet
1. Something that is certain to occur. Based on his grades, it's a pretty good bet that Harry won't be able to graduate on time.
2. A person or thing that is certain to be good or successful. The department felt that she was a good bet for the account manager position.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a good betor
a safe bet
1. If something is a good bet or a safe bet, it is a sensible or useful thing to do or use. If you're after something smart to wear to a friend's wedding, a dark suit has to be a good bet. When you're unfamiliar with your guests' likes and dislikes, chicken is a safe bet for the main course. Note: You can also say that something would be a better bet or a safer bet, meaning that it would be more sensible or useful than another possibility. I was going to buy an apartment but I'm now thinking a house might be a better bet. Basing a drama series on a book is a far safer bet than commissioning a brand new one. Note: You can also say that something is someone's best bet or safest bet, meaning that it is the most sensible or useful thing to do. If you really want to keep your home safe from robbery, your best bet is still to buy a dog.
2. If something is a good bet or a safe bet, it is very likely to happen. With these players, Leeds United look a good bet to reach the final for the first time since 1978. They won't enjoy reading this book; it's a safe bet that few will read more than 100 pages.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012