$20 off JetBlue tickets

To promote its "BillMeLater" payment option, JetBlue is offering

$20 off all tickets

booked through January 31.

Here's how it works: When you book, choose the Bill Me Later option. You'll have to answer a few questions and accept the terms to do this. The discount doesn't display on the JetBlue website at the time of purchase, but the $20 will be automatically credited to your account.

The Bill Me Later option allows you to put off paying for your flight for 90 days. Pay within 90 days and you won't be charged anything extra. However, be aware that you'll be subject to finance charges if you haven't paid in full within that time frame.

Deferred bill paying systems always make me a little nervous, but in this case, if you sign up for the service and then pay promptly, you can save $20 and make this promotion work for you.