If I do janitorial, what mileage can I deduct?

You can deduct the .6 miles between the two offices. Commuting miles are NEVER deductible. The first trip out from home and the last trip back home are commuting miles and are not deductible. See IRS Pub 463 http://www.irs.gov/pub/irs-pdf/p463.pdf for further information on deducting car expenses.

To take a home office deduction your home office must be used solely and exclusively for business use. It must either be the principal place of business or the primary support location for work done off premises. The rules are strict and a HOD is an audit flag. Many folks discover that the record keeping requirements are not worth the minimal tax savings, especially if you own your home. See IRS Pub 587 http://www.irs.gov/pub/irs-pdf/p587.pdf for further information on the business use of your home.

If they get you a fixed $500 a month, they are supposed to add that to your income. Thus any expenses are out of your pocket. Mileage to drive to/from work (or to/from the first work site of the day) is commuting and is never deductible. Other business mileage is, provided you get detailed records. As an employee, the mileage is listed on form 2106. Then reduced by 2% of your AGI. If anything is left, you will be increasing your schedule A. If your schedule A is more than your standard deduction, you itemize. Given the number of miles you think you can claim, be advised, you must also do form 6251 (alternative minimum tax), where the mileage will be added back to your income.

As you are not performing any work at home, you do not have a "home office" for tax purposes.

As such, the trips to office 1 from home and back home from office 2 are non-deductible commuting.

The only deductible mileage you have is the .6 miles between the two offices.

The deduction is the .6 miles between the offices, times the number of times you did this.

You can only deduct for a home office if you have an area of your home that you use REGULARLY and EXCLUSIVELY for your business - sounds real unlikely for a cleaning business with one client. And yes the IRS does send agents out to verify it if you claim it and they audit you, and claiming a home office is audit bait, especially when it doesn't sound likely.

the miles from the first job to the second job

a home office is a room or a specific space that is used exclusively for the business, does not have personal items

ie. this sounds like your office is either your dinner table or a desk you use as well for your personal writing--this is NOT a home office

The deductibility of your mileage doesn't depend on your "home office." If you drive from your home to your worksite, to a second worksite, and home, all of the miles are deductible as business miles at 55.5 cents a mile. Keep a log of all of your trips.

It appears unlikely to me that you would have a home office deduction for your janitorial service with one client. It you need to figure this out, provide details of how you regularly and exclusively use space in your home in connection with this side job.

Business mileage for 2012 is 55 1/2 cents per business mile.

Did you mean, "How much of this can I deduct on my tax return?"

Yes, that is what you meant to say.

So if you do this 250 times a year, and your home office is truly a home office, then you can deduct it all. So that is 2,525 miles.