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SO YOU'RE MARRIED, and your spouse is considering going to work for the first time or returning after a hiatus. Think twice. Unless the primary reason is to pursue professional interests or experience the various other non-monetary joys of employment, it may not pay to work.

After higher taxes and work-related expenses, two salaries probably won't give you anywhere near the cash flow you are anticipating. Throw in the loss of free time and the inevitable stress on family life, and it may not make sense for your honey to put on a suit. Here's why.

Home & Family Taxes - Worksheet

The Marriage Penalty Tax

If your spouse were single, he or she would be taxed like this in 2012: The first $8,700 of taxable income would be taxed at 10%; the next $26,650 at 15%; the next $50,300 at 25%; and the rest at 28%, 33% and 35%, depending on how high the salary climbed.

But, because that spouse is hooked up with you, the tax rules can effectively pile the incremental bucks on top of your pre-existing taxable income, rather than allowing your spouse to start out, like you, paying 10%, then 15%, and so on.

This is in direct contrast to the marriage bonus you now get if only one of you is working but you're married. For example, singles start paying the 28% rate at $85,650. But joint-filers don't jump into that tax bracket until they reach taxable income of $142,700.

Social Security and Medicare Taxes
Remember to add insult to injury by recognizing that Social Security and Medicare taxes will also be sucked out of the second salary. For 2012, the combined rate is 5.65% on the first $110,000 of earnings and 1.45% on the excess. If the second spouse will be self-employed, the rates are even more painful — 13.3% and 2.9% respectively.

State and Local Income Taxes
When evaluating the tax bill you'll owe on that second income, don't forget state income taxes (as well as city taxes in some areas, such as New York City). Most states extract their own version of the marriage penalty.

Totaling Up the Tax Hits
So after you subtract what you'll owe the feds, your city and state, Social Security and Medicare, you may end up bringing home 60% or less of your spouse's new salary. And if the first spouse already earns a healthy income and you live in a high-tax state, the government pickpockets could easily hit you up for 50%.

Don't stop reading. It gets worse. Higher family income also brings the possibility of losing cherished federal tax breaks. For example, the $1,000 per child tax credit begins phasing out when adjusted gross income (AGI) exceeds $110,000. And what about the juicy $2,500 American Opportunity education tax credit? If your AGI exceeds $180,000, you completely lose out. Contributions to those spiffy tax-free Roth IRAs are totally washed out once AGI hits $183,000. The list goes on and on. It takes a Cray supercomputer to calculate the effective tax rate on a second income considering all these factors. The key point is your tax picture is probably much worse than you first thought.

And Those Other Expenses

After dealing with the dismal reality of all the taxes on your spouse's income, go ahead and take a swig of Mylanta. But keep the bottle within reach, because now it's time to get a handle on the other extra — and generally unavoidable — expenses associated with working. These are included in our calculator, and we tried to cover all the bases. Most of the items are self-explanatory, but you need just a few more bits of information on the tax implications.

First, many employers offer "flexible spending accounts" that allow you to reduce your salary by contributing to a child-care spending account. Contributions are limited to $5,000 (in total, for both spouses), and the money must be used to care for children under the age of 13. The contributions are deducted from salary for both federal income and Social Security/Medicare tax purposes, and they permit you to pay for at least part of your child-care expenses with pretax dollars.

Second, if the new job will involve unreimbursed employee business expenses, these may count as "miscellaneous itemized deductions." They are piled up with other miscellaneous outlays, such as fees for investment and tax advice. Then, if the pot exceeds 2% of AGI, you can deduct the excess. So this is no big deal, but it has to be mentioned.

Third, all the other expense items listed on the calculator, with the exception of state and local income taxes, are generally nondeductible "personal expenditures" according to our buddies in Washington. 

Now take a whack at using the calculator to estimate the dollars a second income will net after all taxes and expenses. Not good? Well, it's better to understand this in advance than to meet your financial fate with a smile of blissful ignorance still on your face.