Everything changes when you have a child.

No, I'm not talking about the late-night feedings, the sleepless nights of crying, or the (hopefully) temporary disappearance of your social life. What I mean is that your financial life changes.

You may have had a plan going into the final months before your child was born. If both you and your spouse work, you might have planned for both of you to be back to work within a month or two after your child's birth. Yet when your child actually arrives, you might catch yourself thinking about other possibilities.

Smart economics
From an economic perspective, your first instinct is probably that you'd be a fool not to go back to work. After all, you've gotten used to having two paychecks to support your lifestyle. Now that you face the expenses of raising a child -- which some sources estimate at $10,000 per year or more -- it hardly seems like the time to cut your income voluntarily.

When you're considering the question of whether to have one parent stay at home, however, you have to think about both sides of the equation. Although staying at home will reduce your family income, it may also save you a ton of money that would otherwise go toward day care expenses. Depending on where you live and the level of involvement you want from a nanny or other child-care professional, it's not unheard of to pay upwards of $1,000 per week for the type of full-time care that you could provide free of charge if you chose not to work. That might be plenty of incentive for you or your spouse to stop working.

Opportunity cost
On the pro-career side, the cost of giving up your job to stay at home is more than just the salary you lose. In many cases, you're also sacrificing your prospects for future job advancement. Although explicit gender-based employment discrimination is illegal, labor laws haven't stopped some companies from treating employees who choose families over career opportunities with a degree of skepticism. And while women still face the brunt of such discriminatory practices, men increasingly face the same issues in deciding whether or not to take advantage of paternity leave under the federal Family Leave Act.

Luckily, some companies recognize the value of workers with families. Many large companies, including Microsoft (NASDAQ:MSFT), IBM (NYSE:IBM), and Eli Lilly (NYSE:LLY) offer paid paternity leave along with other parental benefits. But if you decide to stay home beyond your benefit period, then for most employers, all bets are off, and you risk having to start over if you later decide to re-enter the workforce.

Intangible benefits
Of course, whether to stay home with your new child is much more than just an economic decision. Ideally, you wouldn't have to factor finances into your decision at all. But for most of us, practical reality demands that we think about money matters.

By working together with your partner, however, you can reconcile the emotional needs of you and your child with the pragmatic considerations and come up with a solution that will work for everyone. If you consider all the options, you may find that making a good decision is easier than you thought.

Related articles:

Whether you're starting a family or starting to think about retirement, there's always something to think about with your finances. For help with lots of tricky financial situations, check out our personal finance newsletter, Motley Fool Green Light. With Green Light's life-stage approach to financial planning, you'll find plenty of helpful hints tailored specifically to your situation. A free 30-day trial is easy on your pocketbook, too.

Fool contributor Dan Caplinger is lucky to spend as much time as he does with his 2-year-old daughter. He doesn't own shares of the companies discussed in this article. Microsoft is an Inside Value recommendation, while Eli Lilly is an Income Investor pick. The Fool's disclosure policy is like a nanny watching over your portfolio.