Originally Posted by themicah

To expand on emcampbe's answer, points boost affects the value of the points you redeem (in terms of $/point), but doesn't discount the actual $ price of the flight. So if when you search you see a $4,025 airfare that can be purchased for 230,000 points using PointsBoost, it means there is a 1.75x mutliplier on the points (Pointsboost can be anywhere from 1.5x to 2.0x). If you only redeem 100k points at checkout, it will knock $1,750 off the $4.025, and you'll need to charge the remaining $2,275 to a credit card (note that you do NOT have to use the card that the points came from).