DENVER -- When do you buy plane tickets for a trip? Months in advance? Weeks in advance? Days in advance?

I've always heard that you want to buy your tickets three weeks in advance for the best deals. But with the holidays coming, should you buy early or wait?

7NEWS reporter Marc Stewart asked me last week if he should buy his tickets for Thanksgiving now. The airfare was $600, which seemed outrageously expensive to him.

So I told him about Bing.com's price predictor.

Bing is a search engine that works like Google or Yahoo when you need to look up information. But Bing also has something interesting on its home page, a button that says "travel." Click on it to search flights. When you do, it automatically tells you whether you should buy now or wait and the confidence Bing has in its prediction.

When Mark searched flights, Bing told him he should wait to buy his tickets. He did. Two days later, the price dropped from $600 to $300. He bought his tickets and was thrilled to save $300.

I searched for tickets to California for Thanksgiving. I normally pay about $200-$225. Right now, Thanksgiving weekend is $311, but Bing said I should buy now because fares are rising or will remain steady.

Obviously, there are no guarantees.

If you have a deal or freebie, e-mail me Debbie (Debbie@thedenverchannel.com).

Get the latest deals by following me on Twitter @DebbiesDeals. And don't miss a Debbie's Deal! Sign up for a daily e-mail alert by visiting our e-mail alerts page.