Individual tax rebates are getting all the headlines, but the provision of the federal economic stimulus plan that could have the biggest impact might be new rules on business depreciation and equipment write-offs.

As a result, small business advocates say, companies will be encouraged to invest now rather than waiting a few years.

The benefit is two-pronged, said Don Linzer, of Schneider Downs Corporate Finance.

First, Congress doubled the expensing limit for small business, from $125,000 in a year to $250,000, for 2008. That means an extra $125,000 in value can be written off right away, rather than depreciated over time.

But for every dollar over $800,000, the amount of equipment a business can write off decreases equivalently. So, if a business spent $1 million on new equipment, it would be penalized the extra $200,000, meaning it would be able to fully expense just $50,000.

But even if a business spends so much that it wipes out the full expensing benefit, it still gets to write off 50 percent of all new capital investments made this year -- the second prong of the stimulus package, and a benefit to businesses big and small.

It's called the "bonus depreciation" provision, or accelerated depreciation. How it works:

If a business spends $750,000 on new equipment in 2008, it could fully write off the first $250,000 in value, and the balance would written off at a 50 percent rate, meaning the remaining $250,000 in value would be depreciated. So the first $250,000 would be a write off, plus the next $250,000, plus the first-year's depreciation -- say, $35,000. Or, if a business spends less than $250,000, it can write off the whole thing, meaning it can avoid the time and hassle of keeping depreciation records for the next five or seven years.

How will the new rules help?

"That will definitely help the aviation industry," because businesses might be encouraged to make a big-ticket purchase, said Mr. Linzer. "A lot of people are going to buy new jet airplanes."

Because corporate jets are often custom-made, airplane purchases get special consideration under the stimulus package -- if the plane is ordered this year and put into service by Dec. 31, 2009, it qualifies for the write-off laws.

Lee Taddonio, new president of the Pittsburgh's SMC Business Councils trade group, said the new rules will lead to new jobs.

"That's the biggest part of this economic stimulus package," he said. "When they add capital equipment, they're adding jobs."

Both men said the provisions were a bigger deal than the taxpayer rebates, much of which will be spent on utility bills or old credit card debts, according to various polls taken in the last month.

"That's like a drop in the bucket," Mr. Taddonio said. "It might make a little ripple."

But some polling data suggests the new laws likewise may amount to little more than a ripple. The National Federation of Independent Businesses says only 25 percent of small businesses plan to make capital purchases in the next six months.