Q. I took out a $199,000 loan on a $325,000 house in December 2007. Since then, I've doubled every payment of $1,556 and now owe $188,000. Should I continue doing this and pay off the loan in seven years, or should I invest the $1,556 a month in something else?

A. For some people, it is important emotionally to have their house paid for, and it would be great not to have to write out that mortgage check every month. But if your main goal is to maximize savings growth, it's likely that paying off your mortgage early might not accomplish that.

Here's a simple formula to help you decide whether it's smarter to send extra money to your lender or save it for the future.

Multiply your mortgage rate by 1 minus your income tax rate. Compare that return to what you think you would earn on the savings or investment from which you are withdrawing the money. Choose the higher one.

Example: If your mortgage interest rate is 6.5% and your tax rate is 25%, the math is 6.5 times the difference of 1 minus 0.25 (or 6.5 times 0.75).

The result is 4.875%. That's your real mortgage rate when you consider the mortgage tax deduction. So that's the rate you'd want to beat when making other investments.

It's hard to argue against paying off your mortgage early. You can save a ton of money in interest. Assuming that you have a 30-year loan with a fixed rate of 6.5%, those extra payments are going to save you more than $200,000 in interest. With the standard monthly payment, you'd pay $253,831 in interest over 30 years, but with your accelerated payments, you'd pay just $52,588 in interest over 7.5 years.

In reality, however, you are only making 4.875% on that money.

We hope you are not taking this money out of a tax-protected account. If you moved $5,000 of your savings into a Roth IRA each year, your earnings would likely be higher and would grow tax-free until you're forced to take withdrawals when you reach 70 ½. Plus, you always have access to your money. This is probably the best way to grow your retirement nest egg.

For more advice on saving for retirement, take a look at our 6 simple rules for a successful IRA.

If you have a 401(k), be sure that you are contributing the maximum amount. And check out our 7 simple rules for a successful 401(k).

Now is a good time to look at your options. Savers are hard-pressed to make money at the moment because of recent rate cuts by the Federal Reserve. But that will change.

Last summer, a lot of certificates of deposit were paying well over 5%. When that time comes again -- and it will -- a CD paying 5.75% would beat the 4.875% you're making with extra payments. You would get an even better return by "laddering" some high-paying CDs. To see how this can benefit you, check out our CD ladder calculator.

You also could buy mutual funds with a portion of your money. In the long-term, you should be able to make 8% or better on your investment.