So, what am I paying?

With all the sales, discounts, coupons, and clearance deals out there, some shoppers are breaking out their calculators. Others are left scratching their heads.

Brooke Patkin, a University of Pennsylvania student home on break, was working the sales racks at Saks, her cellphone at the ready. But she wasn't planning to call anyone. With Saks and other retailers layering markdowns on top of discounts on top of coupons on top of early-bird savings, Patkin uses the calculator on her cellphone to figure out exactly how much items cost.

"It's nice to know the price before you go try something on," she said as she considered designer clothing that was 60 percent off already-reduced prices, for a total savings of oh, who knows?

As multitiered discounts reach "uncharted territory," according to consumer researcher Britt Beemer, shoppers trying to compute the bottom line can be forgiven for wondering: Are we in the mall or arithmetic class?

"You almost need to be a math major to figure it out," said Ken Perkins, president of Retail Metrics Inc., a market research firm. He provided an example of the kind of calculations confusing some consumers. "You take 40 percent off the original price, then you take 20 percent off that price, which works out to be [a discount of] roughly 52 percent, but the consumer thinks it's going to be 60 percent."

With discounts so deep that retailers are practically giving away merchandise - or, in some cases, literally giving it away, with the purchase of other items - few shoppers are complaining about prices, even though they're not always sure what they are, Perkins added.

"I'm usually pleasantly surprised," said Christine Duncan, an opera student at the Longy School of Music. On a few occasions, she said, she's taken purchases to the register expecting one price, only to learn she's getting an extra discount. "It's confusing, but in my favor."

Sometimes a consumer has no idea how much an item costs because the price tags on identical items carry different prices, an inconsistency that Scott Krugman, a spokesman for the National Retail Federation, attributes to "human error" in the face of rapid and repeated discounting. (So far the NRF has received no reports of retail employees sustaining repetitive motion injuries from re-marking price tags, he said.)

Consider the case of the cornflower-blue summer dress by Jamison. It originally retailed (in some long-ago, now-forgotten universe) for $225 at Saks. When Sheridan Maguire, 55, of Nahant, and her daughter, also named Sheridan, a senior at Bates College, found it, it was selling for 60 percent off the already-reduced price. But what was that price? One dress was marked $134, another $89. To which price did the 60 percent discount apply?

Even the saleswoman was "baffled," Maguire said, but she agreed to take the discount off the lower-priced dress, for a final price of $35. Recounting their story a few minutes after leaving the store, the mother-daughter team remained in disbelief, both at their deal and at the effort involved in securing it.

"It took a lot of work," said the younger Maguire. "But it was worth it," her mother quickly added.

With retailers frantic to unload winter merchandise ahead of the spring season, advertisements for legitimate operations are beginning to sound like infomercials, noted Michael Tonello, author of "Bringing Home the Birkin: My Life in Hot Pursuit of the World's Most Coveted Handbag."

"If you act now, we're going to throw in a Ginsu knife," he joked. "But wait, there's more!"

How much more? Here's a recent online promotion for Lord & Taylor: "60%-80% off winter fashions & accessories when you take an extra 40% to 60% off already-reduced prices and use your 20% savings pass or online promo code: TAKE2."

Got that?

Or this, from Bloomingdales.com: "New Reductions! Plus, take an extra 25-40% off select sale!" At Macy's online, a one-day sale promotion offers savings of 20-65 percent, plus an extra 25 percent savings on clearance items.

Let's forget the fashion police and send in the string theorists.

As the come-ons mount, savvy shoppers are advising novice bargain hunters to study each store's lingo, the better to understand what's on sale, what's not, and how close an item has to be to that "take an additional 25 percent off" sign to qualify for the discount.

"You have to learn their disclaimers," Marcia Smith, 57, of Greensboro, N.C., said as she cruised through the Shops at Prudential Center recently. "Otherwise you can get caught at the register and not get the price you thought you were going to get."

As retail sales continue to slump - December sales were down 1.7 percent from a year ago - some stores are marking down new merchandise much earlier than usual, said Retail Metrics' Perkins, and the discount trend looks like it will continue through the winter, at least. But if this kind of discounting continues for too much longer, he warned, retailers will be creating a monster (namely the consumer), who'll resist ever buying at full price again.

"I'm shopping," Northeastern law student Elliot Chris said as he browsed at the Prudential Center, surrounded by signs offering every kind of discount imaginable. "I don't want to have to read logistics."