Job 1 for Working Moms: Running the Numbers

That second income sounds great, until you start to add up what it will cost you.

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Minimum monthly expense: $175

Housekeeping. You'll have time to clean the house, too? Really? If not, put this down as another cost of doing business—one you might be glad to bear. House cleaning services can run $75 to $100 every two weeks in a major city, depending on house size, unless you persuade your nanny to do it.

Minimum monthly expense: $150

Dog walking. Can Fido make it from the time you leave in the morning until somebody gets home in the afternoon? If not, a dog walker might cost $15 or $20 per walk. Usually, you give walkers a key to your home, and sometimes they'll bring in mail or water plants as well.

Minimum monthly expense: $300

The unforeseen. Namely, taxes. With a second income, your family could move up to a higher tax bracket. Also, while it's nice to anticipate raises and promotions, that might be unrealistic if you're in a part-time or other flexible job. But don't get discouraged. All those expenses merely represent a problem to solve, the very thing many satisfied professionals do all the time. Just another day at the office.