How can I figure out how many points I will receive from a percentage offer?

For an offer that states earn 20% back, if the price is $20, that equals 20,000 points (multiply price paid by 1,000). Then, 20% of 20,000 = 4,000 points (20,000 * 0.2). This means you can expect to receive 4,000 points as a bonus.