NEW YORK (CNNMoney.com) -- Already thinking about all the back-to-school shopping you have to do this year for your kids?

Before you hit the stores, check and see if your state is sponsoring a tax holiday this year.

Over the next few weeks, 13 states and the District of Columbia are offering sales-tax waivers on everything from clothing and shoes to school supplies and computers, according to tax-information firm CCH.

New York, which launched the first-ever program in 1997 and has since offered a sales tax break on certain items year-round, has turned other states onto the concept. This year alone, four new states - Alabama, Maryland, Tennessee and Virginia - will offer their own version of a sales tax holiday.

"They're popular with retail merchants and needless to say, families with back to school expenses," says Dan Schibley, state tax analyst for CCH.

A family living in Hartford, Connecticut that purchases $200 worth of clothing for their children, for example, would save $12 if they shopped during the tax holiday during the third week of August.

Back-to-school spending by American families is expected to reach $17.6 billion this year, up 31 percent from the same period last year, according to a recent study published by the National Retail Federation.

But there is a very real "caveat emptor", or "buyer beware" element to the sales tax holiday. In states such as New Mexico, retailers are not necessarily obligated to participate, so consumers should double check to make sure what they are purchasing is covered by the tax holiday.

Listed below are the different states offering tax holidays, the dates of the tax break and what items qualify.

Dates: August 4-6

Items covered: Clothing priced at $100 or less, school supplies valued at $50 or less and books under $30 each. A single purchase costing $750 of computers, software and school computer supplies is also covered.

Dates: August 20-26

Items covered: Clothing and shoes that sell for under $300. The tax break does not cover athletic or protective clothing and footwear, jewelry, handbags, luggage, umbrellas, wallets and watches.

Dates: August 5-13

Items covered: School supplies, clothing, accessories and shoes that cost $100 or less.

Dates: July 22-30

Items covered: Books, clothes, shoes and certain accessories priced at $50 or less are exempt, as well as school supplies priced at $10 or less per item.

Dates: August 3-6

Items covered: Certain school supplies worth up to $20 each, and clothing and footwear valued at $100 or less are exempt. Computers, computer-related accessories and energy-efficient products priced at $1,500 or less are also exempt.

Dates: August 4-5

Items covered: No sales tax will be collected on clothing or footwear that sells for $100 or less per item, although accessories are not covered.

Dates: August 23-27

Items covered: Clothes and footwear priced at $100 or less.

Dates: August 4-6

Items covered: Clothing and footwear except for certain accessories that are priced at $100 or less, school supplies costing $50 or less, computer software with a taxable value of $350 or less, and personal computers and computer peripherals that retail for $3,500 or less.

Dates: August 4-6

Items covered: Clothing or shoes under $100, computers retailing for $1,000 or less, and any associated monitor, speakers, printer or related items that sells for no more than $500. School supplies priced under $15, bookbags, backpacks, handheld calculators, maps and globes priced under $100 are also covered.

Dates: August 4-6

Items covered: Clothing and school supplies priced at $100 or less are exempt from taxes, as are sports and recreation equipment that costs under $50, and computers priced at $3,500 or less. Clothing accessories, protective equipment, furniture and rentals not covered.

Dates: August 4-6

Items covered: Clothing, clothing accessories, footwear, school supplies, computers, printers, printer supplies, computer software and linens for the bed and bath qualify for the sales tax exemption. Jewelry, cosmetics and furniture, are not covered.

Dates: August 4-6

Items covered: Clothing and school supplies priced at $100 or less, as well as computers retailing below $1,500 are also covered.

Dates: August 4-6

Items covered: Most clothing and footwear priced at less than $100 are exempt from state and local sales taxes. Athletic or protective clothing and footwear are ineligible for the exemption. Clothing accessories and rentals are excluded from the holiday.

Dates: August 4-6

Items covered: Sales of clothing and footwear costing $100 or less are covered under the tax holiday, as well as school supplies valued under $20.

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