Capital One Shopping just rolled out one of its most generous travel offers yet: book a rental car for $100 or more through the portal, and you'll get $100 back in rewards. If your rental lands right around that $100 mark, you're essentially driving off for free.

Here's how it works. Head to CapitalOneShopping.com, log in, and look for the rental car promotion on your offers page. Click "Get this deal," then complete your booking in that same browser session. This part matters: Capital One Shopping tracks the offer through that session, so closing the tab or opening your booking in a new window can void your reward before you even collect it.

A few conditions to know upfront, since the fine print here decides whether this is worth your time:

• You need to spend at least $100 pre-tax in a single rental car transaction.
• This offer is currently targeted at shoppers who haven't booked a rental car through Capital One Shopping before, so check your account to confirm it's showing up for you.
• Rewards post to your account 60 to 90 days after your rental, and they're redeemable for gift cards only, not straight cash. If you don't already have a gift card use in mind, price that into your decision.
• Canceling the rental cancels the reward too.

There's no published end date, but Capital One Shopping offers like this tend to disappear without warning, sometimes within a day or two. If you've got a rental car booking coming up, don't sit on this one.

Worth stacking: Book the rental with a card that already earns bonus rewards on travel, like the Capital One Venture X, and you're layering card rewards on top of the Shopping portal bonus. And if you're not yet a Capital One Shopping member, signing up through a referral link can net you extra rewards before this deal even kicks in.

Bottom line: If you have a rental coming up and don't mind gift card redemptions, this is free money for five extra minutes of booking through the right portal. Just don't dawdle. Complete the booking in one sitting, and don't count on this offer lasting the week.

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