There's a reason the first year of marriage is known as the honeymoon phase. For many newlyweds, it's a time to enjoy each other's company before life's more serious responsibilities kick in. And while you may be inclined to postpone most major decisions in favor of enjoying a year of post-wedding bliss, you can start your marriage right by avoiding these three major mistakes.

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1. Not creating a budget

Even if getting married means being able live off of two incomes instead of just one, it's still imperative that you create a budget. Without one, you'll have a much harder time tracking where your money goes and keeping your expenses in check.

To create a budget, look at how much money you and your spouse bring home each month after taxes. Next, list your monthly expenses line by line, making sure to account for those that may only come up quarterly, like real estate taxes for homeowners. Also remember that not all living costs are fixed; some, like utility bills, fluctuate throughout the year.

Once you've estimated all of your anticipated costs, build some room into your budget for savings and unexpected expenses, such as vehicle repairs or an unusually high medical bill. When you're done, add all of those numbers up and see if your total is less than or equal to your combined take-home pay. If it is, you're in good shape. If not, you'll need to cut corners or make lifestyle changes to ensure that you're not overspending. And the sooner you get your spending in check, the better positioned you'll be to avoid debt and start building some respectable retirement savings.

2. Carrying debt

Whether the source of your debt is student loans, unpaid credit card charges, or the dream wedding that wound up costing more than expected, holding onto that debt can compromise your short-term and long-term financial objectives. The reason? The longer you carry that debt, the more money you'll end up wasting on interest charges.

Let's say you had to finance your nuptials and are now faced with a $20,000 loan at 10% interest. If it takes you five years to pay that off, you'll end up spending an extra $5,500 on interest alone. Now think about what else you could do with $5,500. You could put it toward a down payment on a home, use it to buy a car, or save and invest it for retirement. In fact, if you put that money in stocks, leave it alone for 30 years, and manage to generate an 8% average annual return (which is slightly below the market's average), you'll wind up with an extra $55,000 to pad your nest egg. If you have the means to pay off debt, doing so early on in your marriage will allow you and your spouse to focus on more important and fulfilling goals.

3. Failing to review each other's workplace benefits

One major financial perk of getting married is the ability to take advantage of spousal workplace benefits -- namely, health insurance. If, for example, it costs you $200 a month to get health insurance through your employer but would cost just $80 a month to get added to your spouse's plan, you'd be silly to keep overpaying provided you'd be looking at similar coverage and copays with both plans. You may also be eligible for other benefits through your spouse's company that yours doesn't offer, like life insurance, reduced gym membership fees, and discounted legal services, so it pays to sit down and see what choices you have.

Financial troubles can put a huge strain on even the strongest of marriages, so much so that money has actually been documented as a leading cause of divorce in the U.S. By avoiding a few key pitfalls, you can set yourself up for a lifetime of financial security. And if you're among the lucky ones, maybe even a lifetime of happiness, too.