How to Actually Know You're Getting a Good Deal (Without the Guesswork) We've all been there. You're standing in a store, or scrolling through a sale page at midnight, staring at a big red "50% OFF" sign and trying to do the math in your head. Is it actually 50% off the price you think it is? Does the coupon stack with the sale? And once tax gets added back on, is this even the deal it looked...