Compares an advertised discount against the lowest price you have actually seen.
Formula
advertised saving = (reference price - sale price) / reference price x 100; real saving against your own lowest seen price = (lowest seen - sale price) / lowest seen x 100
Assumptions
The lowest price you have seen is your own observation, which this page cannot verify.
Shipping is added to the sale price before the real saving is worked out.
Limits
A reference price set by the seller is not a market price. Where the law requires it, a reference price must be the lowest price charged in a stated earlier period.