BOSTON — It's official: a sales tax holiday in Massachusetts will be held this weekend.

Gov. Deval L. Patrick today signed a bill that establishes the tax-free shopping for Aug. 11 and 12.

For those two days, the 6.25 percent sales tax is exempted from most items, but the holiday does not include restaurant meals, tobacco and single items that cost more than $2,500.

It would be the state's eighth sales tax holiday in the past nine years. The holiday returned in 2010 after an absence during a state fiscal crisis in 2009.

Jon Hurst, president of the Retailers Association of Massachusetts, said in a recent release that the two-day holiday is similar to a weekend in December, with total sales – including taxed and untaxed sales – in the $500 million range.

Eighteen states across the country have annual sales tax holidays planned for 2012, primarily in August, Hurst said.

The holiday starts the back to school shopping season off early, and is effective in capturing consumers who otherwise might buy goods in tax-free New Hampshire or over the Internet, according to Hurst.



Supporters have also said the holiday works because of the "Boston Tea Party effect," with consumers looking for a break from state taxes, Hurst said.

The sales tax holiday comes with some special rules.

When any single item costs greater than $2,500, the sales tax is assessed on the entire price, not just the amount that exceeds the $2,500, according to a recent advisory by the state Department of Revenue.

Don't worry if you buy multiple items and they collectively cost more than $2,500. As long as each individual item is $2,500 or less, there is no upper limit on the tax -free amount each customer may purchase.

Shoppers should also be aware that if an item of clothing is more than $2,500, the first $175 can be deducted from the tax . If you buy clothing for $2,550 – a wedding dress, for example – tax is due on $2,375.

There is never any sales tax on clothing priced $175 or less, or groceries.

The sales tax holiday is included in a larger economic development bill that has $50 million for a fund to provide matching state grants for research and development into science and technology.

The legislation also creates a $1 million for a talent pipeline through the Massachusetts Technology Collaborative that will provide matching grants aimed at increasing technology sector internships, and another $1 million to support mentoring, advice, incubator space and accelerator programs, a release from the administration said.

The bill also has $5 million for workforce training.