It can be quite a job just figuring IRS rules governing home offices

For many people, commuting to work may mean shuffling from breakfast in the kitchen to a desk in the den.

But for a growing number of those who also want to claim a tax deduction for the expenses of maintaining an office or other home-based workspace, it can also mean wrestling with complex Internal Revenue Service rules.

The deductible expenses can include such items as a portion of a home's utility bills, insurance, and upkeep such as exterior painting or fixing the roof or furnace, all based on the share of the home used for business. Also deductible is depreciation on the area of a house or condo used for business or part of the rent on an apartment.

And there's more. The above expenses -- specifically related to your home -- are lumped together in what the IRS labels a home office deduction. But other out-of-pocket items such as supplies, office equipment, and phone calls are deductible separately when you work at home whether or not you are eligible to claim a home office.

Mark Gentile, of Kingston, is a true believer in the home office. He typically spends two or three hours a day managing his remodeling business from a study in his waterfront home. He considered renting an office but the cost and the commute dissuaded him. And even though he has to hire an accountant to sort out his home-office deductions, he says it's worth it.

''If I have a tough day while out on the jobs, I can come home, have dinner, relax, and then handle the paperwork in my sweats," he says.

Though estimates of how many people work at home vary widely, all point to a big pool of potential deductions. The Census Bureau says 4.5 million people usually worked at home in 2003. But ITAC, a Silver Spring, Md., association that promotes telecommuting, says some 12 million people worked at home almost every day last year, up 41 percent from 2003, and 20 million worked from home at least once a week.

Not everyone qualifies for a deduction and some just avoid the hassle of claiming it. Still, about 2.5 million people deducted a home office for 2002, up 51 percent from five years earlier, according to the IRS, with an average deduction of $2,544, not counting supplies and equipment.

But while it can be enticing to take account of the work you do at home to bulk up federal deductions, and thus also indirectly cut state tax, don't jump the gun. There are restrictions to consider, including limits on deductions if your home-based venture earns little income.

Be wary of con artists selling guidance on how to rack up deductions. The IRS has been winning injunctions, indictments, and access to client lists in legal actions against promoters who sell schemes that employ specious write-offs for minimal or nonexistent business activity.

Among the discredited ploys are hiring family members to do routine household chores, deducting vacations under the guise that everyone is a potential client, and spreading office equipment throughout a home to expand the space claimed as used for business.

''The IRS pays a good deal of attention to the home office deduction because of the potential for abuse," says John Lipold, an IRS spokesman. But, he adds, ''that shouldn't stop a taxpayer from claiming it if he or she is eligible."

The chance of actually facing an IRS audit is low -- only 2.1 percent of self-employed people were audited last year, for example. And though a home office deduction can attract increased IRS scrutiny, accountants privately admit that people vary in how closely they follow the often imprecise rules.

To be deductible a home office must be used regularly and solely for business and must generally be the main place at which you conduct or administer your business -- whether the space is a room or a designated portion of a room. To calculate the percentage of your home used for business, you can measure the square footage of your office and divide that by the total square footage of your home.

Having a key office elsewhere can kill the deduction, and deducting a room in which the family watches TV or you put up guests is a no-no.

To figure out the portion of a home-office expense that is deductible, take the percentage of your home used for business and multiply that, for example, by your annual utility bills and insurance. Other expenses such as office equipment and supplies can be deducted in full if used solely for business, even if you don't have a deductible home office.

And the business must be genuine. ''This can't be a hobby or something you're doing for fun," says San Francisco attorney and author Stephen Fishman, whose book ''Home Business Tax Deductions" helps demystify the rules he himself uses. He says he saves over $2,000 in federal and state tax by deducting expenses for the room he devotes in his apartment to writing.

Self-employed people generally have an easier time qualifying for a deduction than do employees who work from home. An employee's home office must be required by his or her employer, be vital to the job, and be the principal place of work. ''You can't take deductions just because you bring some work home once in a while," cautions Fishman.

Employees who always work at home, especially those who are distant from their employer, will find it simpler to qualify. But even they suffer. Self-employed people can generally deduct qualifying expenses in full. But because employees must claim expenses as a miscellaneous itemized deduction, they typically get to deduct only part of them.

Be prepared to test your brain when considering some deductions. The amount that can be deducted for depreciation, for example, is based on a formula that spreads the write-off over 39 years and depends on what you paid for the home, excluding land. The annual amount will likely be a fraction of 1 percent of the home's cost. And taking the deduction may mean paying extra tax when you sell the home.

Renters can't claim depreciation, but being able to deduct a portion of their rent can be a better deal.

Two suggestions from attorney Fishman:

To bolster the percentage of a home's space used by an office don't count common areas such as hallways and stairs in the home's overall area.

If you regularly meet with clients at home, deduct part of the cost of lawn care if a neat appearance is important.

People adept at doing their own tax returns may be able to handle all this on their own. IRS publication 587 gives the rules. Go to www.irs.gov or call 800-829-3676. But others may want help from an accountant or other tax expert, at least the first time.