United, American, and Southwest are all offering bonuses for shopping through their portals. The bonuses are in addition to what you’d already be earning by shopping through the portal. Shopping portals allow you to earn miles by making your normal online purchases through your favorite online stores. Just by starting at the loyalty program’s portal and using its link to your favorite online retailer, you can get extra miles for your purchases.

With each holiday shopping promotion, the more you spend, the higher your return is.