SHOPPING MATH GUIDE
20% Extra vs. 20% Off
See why 20% more product is not the same as 20% off, with a simple unit-price comparison.
GUIDES
Make sense of store promotions
Short explanations, worked examples, and calculators for the deals that are hard to compare at a glance.
SHOPPING MATH GUIDE
Buy 3, Get 1 Free: Percent Off
Learn why buying three items and getting one free works out to an effective 25% discount.
SHOPPING MATH GUIDE
How to Calculate Shrinkflation
Use unit prices to measure the real price increase when a package gets smaller, more expensive, or both.