WHEN it comes to wooing wary shoppers, many retailers are playing the percentages.

Campaigns for stores, from giant chains to mom-and-pops, are promoting sales that are frequently expressed in percentages off from regular prices. Twenty or 25 percent off, once considered a hefty discount, is practically nothing nowadays, as most consumers must be enticed further to open their wallets or purses.

How willing shoppers are to shop is important as retailers approach the start of the crucial Christmas season. To prime the pump, ads are routinely proclaiming savings of 50, 60 and even 70 percent off. In some instances, the discounts are going as high as 85 percent.

Some retailers are subtracting atop subtraction by offering an “extra” percentage off merchandise, typically items that had been marked down earlier.

For instance, Bloomingdale’s, part of Macy’s Inc., promoted in newspaper ads on Sunday “an extra 30 percent-40 percent off” the reduced prices on clothing, handbags, accessories and jewelry for “a total savings of 40 percent-75 percent off original prices.”