Levin: We all want certainty in our personal finances, but there is science involved

If you don't smoke, get exercise, eat healthy and stay out of the sun, you will live to be 93.2 years. Except you might not.

Because our lives aren't math, they are science. Math proves things, while science disproves things.

When it comes to our financial planning, we all want math. And there certainly is some of it. Taxes are pretty much math, even though there may be a bit of science when it comes to deductions. Social security and pensions are math, but how long you are going to collect each is science. What you earn on savings is math.

But really, financial planning is mostly science. There are so many things that influence your outcomes. You need to embrace the uncertainty of science to make decisions that will most likely, and often inevitably, lead you to the results you want.

All sorts of studies indicate how much you can spend when you retire, but obviously the biggest influence will be how long you will live.

The studies provide important guidance for you, but they can never be definitive. Here are some common-sense considerations. You want to drive down your fixed costs as much as possible when you retire because that enables you to spend less if you feel poor.

When the markets are falling, you shouldn't delay your health insurance or mortgage payments, but you might not go on a trip. If most of your retirement income is coming from pensions and social security and your fixed costs are generally covered, your investments serve to enhance your lifestyle, magnify your giving or leave an estate. Driving down fixed costs increases your options.

But there also is a science around on what you want to spend. Some of us are so worried about running out of money that we underspend on the things that are important to us. Advertising uses science to encourage us to want things we don't necessarily need, but there also is science showing that if we are able to pause before we buy something, there is a higher likelihood we won't buy it at all.

My wife and I have a three-day rule for big decisions to protect us from our impulses. Science also indicates that we value experiences more than things, but for some, things are experiences. For the person who loves to cook, a wonderful kitchen creates an experience. Define what outcome your purchases are intended to give you as a way to determine their value.

Using science to guide your decisionmaking won't result in math's absolutes, but your results can still be meaningful.

Spend your life wisely.

Ross Levin (ross@accredited.com) is a founding principal and president of Accredited Investors Inc., Edina.